Systems, methods, and devices for partition management of storage resources

ABSTRACT

A method of operating a storage system may include allocating a first partition of a tier of storage resources to a first client, wherein the tier operates at least partially as a storage cache, allocating a second partition of the tier of the storage resources to a second client, monitoring a workload of the first client, monitoring a workload of the second client, and reallocating the first partition of the tier of the storage resources to the first client based on the monitored workload of the first client and the monitored workload of the second client. The method may further include reallocating the second partition of the tier of the storage resources to the second client based on the monitored workload of the first client and the monitored workload of the second client.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to, and the benefit of, U.S.Provisional Patent Application Ser. No. 63/088,447 titled “Systems,Methods, and Devices for Disaggregated Storage with PartitionManagement” filed Oct. 6, 2020 which is incorporated by reference.

TECHNICAL FIELD

This disclosure relates generally to data processing, and morespecifically to systems, methods, and devices for partition managementof storage resources.

BACKGROUND

Storage systems may divide storage resources into partitions for use byone or more storage clients.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not constitute prior art.

SUMMARY

A method of operating a storage system may include allocating a firstpartition of a tier of storage resources to a first client, wherein thetier operates at least partially as a storage cache, allocating a secondpartition of the tier of the storage resources to a second client,monitoring a workload of the first client, monitoring a workload of thesecond client, and reallocating the first partition of the tier of thestorage resources to the first client based on the monitored workload ofthe first client and the monitored workload of the second client. Themethod may further include reallocating the second partition of the tierof the storage resources to the second client based on the monitoredworkload of the first client and the monitored workload of the secondclient. The first partition may be reallocated based on an input and/oroutput (I/O) demand of the workload of the first client. The firstpartition may be reallocated based on an I/O demand of the workload ofthe second client. The first partition may be reallocated based on aperformance change estimation of the workload of the first client. Thefirst partition may be reallocated based on a performance changeestimation of the workload of the second client. The first partition maybe reallocated based on a read-write ratio of the workload of the firstclient. The first partition may be reallocated based on a working set ofthe workload of the first client. The first partition may be reallocatedbased on a working volume of the workload of the first client.

A system may include a storage layer comprising a tier of storageresources configured to operate at least partially as a storage cache,an application server layer configured to process I/O requests for thestorage layer from a first client and a second client, monitor logicconfigured to monitor a workload of the first client and a workload ofthe second client, decision logic configured to determine an adjustedpartition scheme based on the monitored workload of the first client andthe monitored workload of the second client, and partition logicconfigured to allocate a first partition of the tier of storageresources to the first client, allocate a second partition of the tierof storage resources to the second client, and reallocate the firstpartition of the tier of storage resources to the first client based onthe adjusted partition scheme. The monitor logic may include an I/Ofilter. The monitor logic may include a hypervisor. The applicationserver layer may include an interface configured to provide astandardized I/O interface to the first client and the second client.

A method of partitioning a tier of storage resources may includedetermining a read working volume and a write working volume of a firstclient of the tier and a second client of the tier, determining aworkload type based on the read working volume and the write workingvolume, and partitioning the tier of storage resources between the firstclient and the second client based on the workload type. The method mayfurther include determining a read ratio based on the read workingvolume and the write working volume, and determining the workload typebased on the read ratio. Determining the workload type based on the readratio may include comparing the read ratio to a threshold. The methodmay further include determining a working set size based on the workloadtype, and partitioning the tier of storage resources between the firstclient and the second client based on the working set size. The methodmay further include determining a working volume size based on theworkload type, and partitioning the tier of storage resources betweenthe first client and the second client based on the working volume size.

A method of detecting a burst of accesses of a tier of storage resourcesmay include monitoring a workload of the tier of storage resources,determining a burst degree of the workload, and detecting the burst ofaccesses based on the burst degree. Detecting the burst of accessesbased on the burst degree may include comparing the burst degree to aburst threshold. Determining a burst degree of the workload may includedetermining a read intensity of the workload. Determining the burstdegree of the workload may include determining a change in a workingvolume of the workload, and calculating the burst degree based on thechange in the working volume of the workload. Determining the burstdegree of the workload may include determining a change in a working setof the workload, and calculating the burst degree based on the change inthe working set of the workload.

A method of partitioning a tier of storage resources may includemonitoring a workload of the tier of storage resources, determining afirst cache demand for a first client based on the monitored workload,determining a second cache demand for a second client based on themonitored workload, allocating a first partition of the tier of storageresources to the first client based, at least in part, on the firstcache demand, and allocating a second partition of the tier of storageresources to the second client based, at least in part, on the secondcache demand. The first partition and the second partition may beallocated, at least in part, in proportion to the first cache demand andthe second cache demand. Determining the first cache demand may includedetermining a first workload amount for the first client, anddetermining the second cache demand may include determining a secondworkload amount for the second client. The first workload amount and thesecond workload amount may be determined, at least in part, based on aread intensity of the monitored workload. The first workload amount maybe determined based, at least in part, on a working volume size of thefirst client, and the second workload amount may be determined based, atleast in part, on a working volume size of the second client. The firstworkload amount may be determined based, at least in part, on a workingset size of the first client, and the second workload amount may bedetermined based, at least in part, on working set size of the secondclient. The method may further include weighting the first workloadamount, and weighting the second workload amount. The method may furtherinclude sorting the first client and the second client based on theweighted first workload amount and the second weighted workload amount.The method may further include allocating the first partition of thetier of storage resources to the first client based, at least in part,on the weighted first workload amount, and allocating the secondpartition of the tier of storage resources to the second client based,at least in part, on the weighted second workload amount.

A method of partitioning a tier of storage resources may includedetermining a first partition plan for a first client and a secondclient for the tier of storage resources, determining a first expectedcache hit amount based on the first partition plan, determining a secondpartition plan for the first client and the second client for the tierof storage resources, determining a second expected cache hit amountbased on the second partition plan, and selecting one of the firstpartition plan or the second partition plan based on the first expectedcache hit amount and the second expected cache hit amount. The methodmay further include determining a first expected hit ratio for the firstclient based on the first partition plan, determining a second expectedhit ratio for the second client based on the first partition plan,determining a first expected working volume for the first client basedon the first partition plan, and determining a second expected workingvolume for the second client based on the first partition plan.Determining the first expected cache hit amount may include determininga weighted sum of the first expected hit ratio and the first expectedworking volume for the first client and the second expected hit ratioand the second expected working volume for the second client. The methodmay further include determining a third partition plan for the firstclient and the second client for the tier of storage resources,determining a third expected cache hit amount based on the thirdpartition plan, and selecting one of the first partition plan, thesecond partition plan, or the third partition plan based on the firstexpected cache hit amount, the second expected cache hit amount, and thethird expected cache hit amount.

A method of determining an expected cache hit ratio for a client of atier of storage resources may include recording I/O transactions by theclient for the tier of storage resources, determining a reuse distancebased on the recorded I/O transactions, and determining the expectedcache hit ratio based on the reuse distance. Determining the expectedcache hit ratio may include determining a distribution function of reusedistances based on the recorded I/O transactions, and determining theexpected cache hit ratio based on the distribution function. Theexpected cache hit ratio may be based on a difference between a reusedistance and a cache size.

A method of determining an expected working volume for a client of atier of storage resources may include recording I/O transactions by theclient for the tier of storage resources, determining a weighted averageof the recorded I/O transactions, and determining the expected workingvolume based on the weighted average. The weighted average may beexponentially weighted.

A method of re-partitioning a tier of storage resources may includeallocating a first partition of the tier of storage resources to aclient, wherein the tier operates at least partially as a storage cache,allocating a second partition of the tier of storage resources to theclient, wherein the size of the second partition may be greater than thesize of the first partition, and passively updating the secondpartition. Passively updating the second partition may include updatingthe second partition based on one or more I/O transactions of a workloadof the client. The second partition may be allocated based on apartition adjustment and content update window.

A method of prefetching data for a tier of storage resources may includeallocating a first partition of the tier of storage resources to aclient, wherein the tier operates at least partially as a storage cache,determining a pattern of I/O request sizes for the client, allocating asecond partition of the tier of storage resources to the client, whereinthe size of the second partition may be greater than the size of thefirst partition, and prefetching data for the second partition using aprefetch data size based on the pattern of I/O request sizes. Theprefetch data size may include a top I/O size popularity of the client.The method may further include applying an amplification factor to theprefetch data size.

A method of partitioning a tier of storage resources may includeallocating a first partition in a first zone of the tier of storageresources to a first client based on preknowledge of a characteristic ofthe first client, and allocating a second partition in a second zone ofthe tier of storage resources to a second client based on preknowledgeof the characteristic of the second client. The method may furtherinclude adjusting a size of the first zone and a size of the secondzone. The size of the first zone and the size of the second zone may beadjusted proportionally. The size of the first zone may be adjustedbased on a first demand amount of the first zone, and the size of thesecond zone may be adjusted based on a second demand amount of thesecond zone. The first zone may include a read-intensive zone, and thesize of the first zone may be adjusted based on a working set size. Thefirst zone may include a write-intensive zone, and the size of the firstzone may be adjusted based on a working volume size. The first zone mayinclude a read-write-mixed zone, and the size of the first zone may beadjusted based on a working volume size. The characteristic may includeat least one of a read ratio, a working volume size, or a working setsize.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures are not necessarily drawn to scale and elements of similarstructures or functions may generally be represented by like referencenumerals or portions thereof for illustrative purposes throughout thefigures. The figures are only intended to facilitate the description ofthe various embodiments described herein. The figures do not describeevery aspect of the teachings disclosed herein and do not limit thescope of the claims. To prevent the drawing from becoming obscured, notall of the components, connections, and the like may be shown, and notall of the components may have reference numbers. However, patterns ofcomponent configurations may be readily apparent from the drawings. Theaccompanying drawings, together with the specification, illustrateexample embodiments of the present disclosure, and, together with thedescription, serve to explain the principles of the present disclosure.

FIG. 1 illustrates an embodiment of a storage system architecture inaccordance with example embodiments of the disclosure.

FIG. 2 illustrates an example embodiment of a storage systemarchitecture in accordance with example embodiments of the disclosure.

FIG. 3 illustrates an embodiment of a storage system softwarearchitecture in accordance with example embodiments of the disclosure.

FIG. 4 illustrates example embodiments of inputs and outputs for aninterface for file-oriented storage operations in accordance withexample embodiments of the disclosure.

FIG. 5 illustrates example embodiments of inputs and outputs for aninterface for object-oriented storage operations in accordance withexample embodiments of the disclosure.

FIG. 6 illustrates an example embodiment of a storage layer inaccordance with example embodiments of the disclosure.

FIG. 7 illustrates an example embodiment of a workflow architecture fora partition manager system in accordance with example embodiments of thedisclosure.

FIG. 8 illustrates example embodiments of temporal windows for aworkflow for a partition manager system in accordance with exampleembodiments of the disclosure.

FIG. 9 illustrates an example embodiment of a mixed read and writeworkload in accordance with example embodiments of the disclosure.

FIG. 10 illustrates an example embodiment of a mixed read and writeworkload in accordance with example embodiments of the disclosure.

FIG. 11 illustrates an example embodiment of a burst calculation andburst detection method in accordance with example embodiments of thedisclosure.

FIG. 12 illustrates an example embodiment of a method for a partitioningmethod for a bursty workload in accordance with example embodiments ofthe disclosure.

FIG. 13 illustrates an example embodiment of a CDF curve for a hit ratioestimation operation in accordance with example embodiments of thedisclosure.

FIG. 14 illustrates an example embodiment of a partition and contentupdate workflow in accordance with example embodiments of thedisclosure.

FIG. 15 illustrates an example embodiment of an adaptive prefetch sizeadjustment method in accordance with example embodiments of thedisclosure.

FIG. 16 illustrates an example embodiment of an adaptive prefetch sizeadjustment method in accordance with example embodiments of thedisclosure.

FIG. 17 illustrates an example embodiment of a preknowledge-based zoningmethod in accordance with example embodiments of the disclosure.

FIG. 18 illustrates an example embodiment of a preknowledge-based zoningworkflow in accordance with example embodiments of the disclosure.

FIG. 19 illustrates an embodiment of a method of operating a storagesystem in accordance with example embodiments of the disclosure.

DETAILED DESCRIPTION 1. Introduction 1.1 Overview

A storage system having one or more tiers of storage resources maypartition one or more of the tiers into individual partitions, each ofwhich may be accessed by one of multiple storage clients. In someembodiments, a partition manager system in accordance with exampleembodiments of the disclosure may periodically and/or dynamically adjustthe partition size for one or more of the tiers for one or more of thestorage clients. The partition adjustment process, which may be referredto as re-partitioning, may improve or optimize the overall performanceof a storage system and/or ensure fairness to storage clients. In someembodiments, a partition manager system in accordance with exampleembodiments of the disclosure may provide automated re-partitioningdecision making and/or operations based on one or more factors such asruntime workload analysis, performance improvement estimation,quality-of-service (QoS), service level agreements (SLAs), and/or thelike.

1.2 Storage Workloads

In some embodiments of storage systems used for game streaming, a largepercentage of gameplay input and/or output (I/O) workloads may beread-intensive or even read-only. Some embodiments of partition managersystems and methods in accordance with example embodiments of thedisclosure may provide different cache re-partitioning strategies basedon the differences between read-intensive and non-read-intensiveworkloads.

In some embodiments of storage systems, workloads for different clientsmay have different behaviors, and even the same workload for one clientmay vary during runtime. Some embodiments of partition manager systemsand methods in accordance with example embodiments of the disclosure mayequally assign the top-tier storage resources to each client and/orallow clients to conduct free competition for top-tier storage resourcesbased on client demands. However, in some embodiments, either or both ofthese techniques may underutilize storage resources, including top-tierstorage resources. Some embodiments of partition manager systems andmethods in accordance with example embodiments of the disclosure mayperiodically capture and/or predict I/O changes to adaptively reallocatestorage resources, including top-tier resources, as well as usingdifferent partitioning methodologies for workloads having differentburst levels. Depending on the implementation details, this may improvestorage cache hit ratios anchor reduce I/O management costs.

In some embodiments of storage systems, I/O size distributions may bedifferent for different workloads. Some embodiments of partition managersystems and methods in accordance with example embodiments of thedisclosure may use an adaptive I/O size for first-second-tier prefetchoperations. Depending on the implementation details, this may increaseoverall hit ratios and/or reduce I/O latencies.

In some embodiments of storage systems, during a deployment stage, theremay not be sufficient client runtime data available to implement aneffective allocation of top-tier cache storage to clients, Someembodiments of partition manager systems and methods in accordance withexample embodiments of the disclosure may use preknowledge (e.g.,prior-knowledge) of clients, for example, from a client pattern library,vendor selection hardware and/or software, QoS, SLA, and/or the like, toperform an initial partition of top-tier cache storage to clients. Insome embodiments, different clients may be placed into differentworkload zones based on preknowledge of one or more factors such asworkload read ratio, workload working set size, and/or the like. In someembodiments, zoning may be physical zoning, virtual zoning, and/or anycombination thereof. In physical zoning, granularity may be greater thanor equal to the size of a storage device (e.g., grouping multiplestorage devices into a zone. In virtual zoning, granularity may be lessthan or equal to a storage device (e.g., zoning inside a storagedevice).

1.3 Partition Management

Some embodiments of partition management systems and/or method inaccordance with example embodiments of the disclosure may periodicallyand/or dynamically re-partition one or more tiers (e.g., a top-tier) ofa storage system that may be shared by multiple clients. Someembodiments may allocate top-tier storage resources to clients that needit (based, for example, on dynamic I/O demands) and/or to clients thatmay benefit from it the most (based, for example, on estimates ofperformance improvement). The allocation may be based, for example, onanalyzing runtime workload parameters such as read-write ratios, workingset changes, working volume changes, and/or the like.

Some embodiments may provide a partition optimization framework that maytake into consideration various factors for some or all storage clientssuch as changes in workload during a recent workload monitoring window,the weight of one or more clients (e.g., base on QoS, SLAs and/or thelike), the estimated hit ratio that may be expected if a partition sizeis increased or decreased, and/or the like.

Some embodiments may provide a burst detection method to determinewhether a current workload is bursty. If the current workload is bursty,the system may not have adequate time to apply a partition optimizationframework before an I/O burst arrives. Thus, for bursty workloads, anaggressive partitioning scheme may be used to quickly partition atop-tier of storage between clients. In some embodiments, an aggressivepartitioning scheme may adjust partitions proportionally based on recentdemand as determined, for example, by a working volume size (fornon-read-intensive workloads) or a working set size (for read-intensiveworkloads).

Some embodiments may implement a technique to perform an initialpartitioning by separating clients into different zones based onpreknowledge during a deployment stage. Depending on the implementationdetails, a zone-based partitioning technique may reduce device-sidewrite amplification, over-provisioning, total cost of ownership, and/orthe like, and may improve latency, throughput, predictability, and/orthe like.

1.4 Storage Types

Partition management systems, methods, apparatus, workflows, and/or thelike in accordance with example embodiments of the disclosure may beused with any type of storage such as direct-attached storage (DAS),storage area networks (SANs), disaggregated storage, and/or the like.

In DAS systems in accordance with example embodiments of the disclosure,storage devices such as solid state drives (SSDs) and hard disk drives(HDDs) may he attached to a single server. This configuration mayprovide relatively high performance for any workloads running on thatserver. The storage device capacity and/or performance may be availableto that server, and capacity and/or performance may scale-up (addingdrives to the server) or scale-out (by adding additional servers).

In SAN systems in accordance with example embodiments of the disclosure,storage devices may be arranged in a storage array that may beprovisioned to be available one or many servers on a network. A SANsystem may allocate storage to many servers (e.g., dozens or hundreds ofservers), which may increase capacity utilization.

In some embodiments of cloud computing in accordance with exampleembodiments of the disclosure, client devices may be implemented aslight terminals that may assign tasks and/or gather results of assignedtasks, while heavy computational tasks may be performed on remotedistributed server clusters. This light-terminal/heavy-datacenterstructure may involve high availability storage systems. In someembodiments, storage input and/or output (I/O) may he a bottleneck, forexample, in datacenters.

In disaggregated storage systems in accordance with example embodimentsof the disclosure, some number of storage devices may function as alogical pool of storage that may be allocated to any server on anetwork, for example, over a high-performance network fabric. In someembodiments, disaggregated storage system may provide the performance oflocal storage with the flexibility of SAN, and/or may be dynamicallyreconfigurable which may enable physical resources to he reconfigured toimproved or maximize performance and/or reduce latency.

2. Architecture

FIG. 1 illustrates an embodiment of a storage system architecture inaccordance with example embodiments of the disclosure. The architectureillustrated in FIG. 1 may represent hardware, software, workflow, and/orany combination thereof.

The embodiment illustrated in FIG. 1 may include an application serverlayer 104 and a storage layer 106. The storage layer 106 may include anynumber and/or types of storage resources that may be configured as apool having one or more tiers, including those described below. Forexample, a first tier of storage resources may operate as a storagecache for one or more other tiers of storage resources. One or more ofthe tiers may be divided into partitions that may be allocated to one ormore of the storage clients 102.

The application server layer 104 may include any number and/or types ofcompute and/or I/O resources, including those described below,configured to enable the one or more storage clients 102 to access thepool of storage resources in the storage layer 106.

The application server layer 104 may be connected to one or more of thestorage clients 102 through one or more connections 108. The applicationserver layer 104 may be connected to the storage layer 106 through oneor more connections 110. The connections 108 and 110 may be implementedwith any number and/or type of networks, interconnects, and/or the like,including those described below.

The application server layer 104 and storage layer 106 may include logic140 and 142, respectively, that may be used to implement any functionsperformed by the respective layers such as monitoring operations of thesystem, making decisions, performing system operations, performingcalculations, and/or the like. In some embodiments, logic 140 and 142may implement any of the techniques disclosed herein such as monitoringworkloads of one or more tiers of the storage layer 106, determining aread intensity of a workload, detecting bursts in I/O accesses,determining working volumes, determining working sets, determining are-partitioning strategy, partitioning one or more tiers of a storagelayer, implementing a partitioning strategy, implementing a clientzoning technique, and/or the like.

The logic 140 and 142, as well as any of the methods, techniques,processes, and/or the like described herein, may be implemented withhardware, software, or any combination thereof. For example, in someembodiments, any of the logic 140 and 142 may be implemented withcombinational logic, sequential logic, one or more timers, counters,registers, state machines, complex programmable logic devices (CPLDs),field programmable gate arrays (FPGAs), application specific integratedcircuits (ASICs), complex instruction set computer (CISC) processorsand/or reduced instruction set computer (RISC) processors, and/or thelike executing instructions stored in volatile memories such as dynamicrandom access memory (DRAM) and/or static random access memory (SRAM),nonvolatile memory such as flash memory, and/or the like, as well asgraphics processing units (GPUs), neural processing units (NPUs), and/orthe like.

The operations and/or components described with respect to theembodiment illustrated in FIG. 1, as well as all of the otherembodiments described herein, are example operations and/or components.In some embodiments, some operations and/or components may be omittedand/or other operations and/or components may be included. Moreover, insome embodiments, the temporal and/or spatial order of the operationsand/or components may be varied. Although some components may beillustrated as individual components, in some embodiments, somecomponents shown separately may be integrated into single components,and/or some components shown as single components may be implementedwith multiple components.

2.1 Data Center Architecture

FIG. 2 illustrates an example embodiment of a storage systemarchitecture in accordance with example embodiments of the disclosure.The system illustrated in FIG. 2 may include a cloud client layer (CCL)202, an application server layer (ASL) 204 and a storage layer 206. Insome embodiments, the storage layer 206 may be implemented as a backendstorage layer (BSL). The dent cloud layer 202 and application serverlayer 204 may be connected, for example, by one or more networks 208.The application server layer 204 and storage layer 206 may be connected,for example, by an I/O path 210.

In some embodiments, the client cloud layer 202 may include any numberand/or types of cloud client devices 203 (e.g., heterogeneous devices)which may connect to and/or between the client cloud layer 202 throughany number and/or types of networks, and may eventually connect to theapplication server layer 204 through one or more of the networks 208.Examples of cloud client devices 203 may include desktop and/or laptopcomputers, servers, smart phones, tablets, printers, scanners, internetconnected appliances and/or the like. The client cloud layer 202 mayhandle any number of the following conditions and/or processes: I/Ocongestion, delays and/or timeouts, workload surge, dropped packets,and/or the like.

The one or more networks 208 may be implemented with any number and/ortypes of network including local area networks (LANs), metropolitan areanetworks (MANs), wide area networks (WANs), and/or the like, based onany number and/or types of network hardware, software, protocols, and/orthe like. Examples of network types may include Ethernet, InfiniBand,Fibre Channel, Wi-Fi, Bluetooth, and/or the like.

In some embodiments, the application server layer 204 may be implementedwith any number and/or types of server apparatus including motherboards,switchboards, I/O cards and/or modules, backplanes, midplanes, networkinterface cards (NICs), and/or the like configured in one or morechassis, server racks, groups of server racks, data rooms, datacenters,edge datacenters, mobile edge datacenters, and/or any combinationsthereof, and/or the like. The application server layer 204 may handleany number of the following conditions and/or processes: resourceallocation, data contention, I/O delays and/or errors, I/O waitingand/or queuing, I/O timeouts, locking (e.g., excessive locking), systeminstability, central processing unit (CPU) overhead, and/or the like.

The I/O path 210 may be implemented with any number and/or types ofconnections including one or more interconnects and/or protocols such asPeripheral Component Interconnect Express (PCIe), Compute Express Link(CXL), Advanced eXtensible Interface (AXI), and/or the like, one or morestorage connections and/or protocols such as Serial ATA (SATA), SerialAttached SCSI (SAS), Non-Volatile Memory Express (NVMe), and/or thelike, one or more network connections and/or protocols such as Ethernet,Fibre Channel, InfiniBand, and/or the like, as well as combinationsthereof such as NVMe over Fabric (NVMe-oF), and/or the like.

The storage layer 208 may be implemented with any number and/or types ofstorage apparatus such as solid state drives (SSDs), hard disk drives(HDDs), optical drives, drives based on any type of persistent memorysuch as cross-gridded nonvolatile memory with bulk resistance change,and/or the like, and/or any combination thereof. Such apparatus may beimplemented in any forms and/or configurations, for example, as storagedevices having form factors such as 3.5 inch, 2.5 inch, 1.8 inch, M.2,and/or the like, and/or using any connector configurations such as SATA,SAS, U.2, and/or the like. Some embodiments may be implemented entirelyor partially with and/or within a server chassis, server rack, dataroom, datacenter, edge datacenter, mobile edge datacenter, and/or anycombinations thereof, and/or the like.

In some embodiments, the combination of the application server layer 204and the storage layer 206 may implement a datacenter. Thus, depending onthe implementation details, the application server layer 204 and thestorage layer 206 may be considered a near-field arrangement, whileclient cloud layer 202 and application server layer 204 may beconsidered a far-field arrangement.

The embodiment illustrated in FIG. 2 may further include one or morepartition manager applications 212 which may interface, for example,between the client cloud layer 202 and application server layer 204and/or between the application server layer 204 and the storage layer206. In some embodiments, the partition manager applications maydetermine how to allocate one or more tiers of storage resources (e.g.,a top-tier of storage resources) in the storage layer 206 to differentclients (e.g., cloud clients 203) and/or and their applications.

Although the principles of this disclosure are not limited to anyparticular implementation details, for purposes of illustration, someexample embodiments may be implemented as follows. A client cloud layer202 may be connected to an application server layer 204 through one ormore LANs, MANS, or WANs, implemented with multi-Gb Ethernet connections(e.g., 10 Gb/25 Gb/40 Gb/100 Gb Ethernet). An application server layer204 may employ one or more PCIe interconnects which, using PCIeGeneration 4 (PCIe Gen 4), may deliver more than 8 GB/sec of throughput.An application server layer 204 may be connected to a storage layer 206using one or more NVMe-oF connections through which, for example, anNVMe storage device may deliver millions of input and/or outputoperations per second (IOPS). Depending on the implementation details,such embodiments may reduce or eliminate bandwidth limitations and/orbottlenecks.

2.2 Software I/O Path Architecture

FIG. 3 illustrates an embodiment of a storage system softwarearchitecture in accordance with example embodiments of the disclosure.The software architecture illustrated in FIG. 3 may be used, forexample, with the storage system architecture illustrated in FIG. 2, butit may be used with other systems as well. The embodiment illustrated inFIG. 3 may include a cloud client layer (CCL) 302, an application serverlayer (ASL) 304, and a storage layer (BSL) 306.

In some embodiments, the client cloud layer 302 may include one or moreclients 303, each of which may run one or more operating system (OS) 316and one or more applications (APP) 314. In this example, there may be Nclients: Client 1, Client 2. . . Client N. In some embodiments, clients303 may be modeled as operating systems 316 and/or applications 314.Depending on the implementation details, a client 303 may have one ormore operating systems 316 and/or applications 314. Moreover, eachoperating system 316 may host any number of applications 314.

Depending on the implementation details, some or all of the clients maybe isolated from each other. Examples of clients may include any of theindividual clients 203 illustrated in FIG. 2, as well as one or morevirtual machines (VMS) that, for example, may be rented to a user from acloud service vendor. Depending on the implementation details, clients303 such as VMs may have different workload characteristics based, forexample, on user applications, and thus they may have different levelsof sensitivity to storage I/O speeds.

Each client 303 (which may also be referred to as a storage client) maybe connected to the application storage layer 304 through a networkconnection 318 which may be implemented, for example, using any numberand/or types of networks connections such as those described above withreference to FIG. 2. For VMs, a network connection may be implemented asa virtual network connection.

The application server layer 304 may include an I/O filter 320, apartition manager interface 322, and a partition decision maker 324. Insome embodiments, the I/O filter 320 may be implemented with, or as partof, one or more hypervisors which may also be used, for example, toimplement client VMs. The I/O filter 320 may collect I/O relatedstatistics for the clients and provide these statistics to the partitiondecision maker 324. In embodiments that include a hypervisor, one ormore VMs may be hosted using hypervisor software which may have a builtin I/O filter function (e.g., “IOFilter( )”) that may be used to handleI/O requests and/or collect I/O statistics. For purposes ofillustration, the I/O filter 320 in the embodiment illustrated in FIG. 3may be shown as a hypervisor, but other types of I/O filters may beused.

In some embodiments, the partition manager interface 322 may provide astandard I/O interface for one or more of the clients 303. Depending onthe implementation details, the partition manager interface 322 mayprovide operations for file-based systems, key-value object storagesystems, and/or any other type of storage system and/or combinationsthereof, as described in more detail below. The partition managerinterface 322 may interface with the storage layer 306 through an I/Opath 326 that may be implemented using any number and/or types ofconnections such as those described with reference to the I/O path 210illustrated in FIG. 2.

The partition decision maker 324 may make decisions at various times,for example, at periodic intervals, to trigger re-partitioning of one ormore tiers of the storage layer 306. Re-partitioning may be based, forexample, on predicted client performance if one or more clients aremigrated to other tiers as well corresponding migration overhead.

The storage layer 306 may operate one or more tiers 328 of storagedevices arranged, for example, as a pool of storage resources that maybe allocated between different clients. In this example there may be Mtiers: Tier 1, Tier 2, . . . Tier M. In some embodiments, differenttiers may have different characteristics, for example, for tradeoffsbetween access speed, capacity, and/or the like. In the embodimentillustrated in FIG. 3, all of the storage devices may be illustrated asvarious types of SSDs, but any type and/or configuration of storageresources may be used.

The storage layer 306 may also include a partitioner 330 which, based ona partition decision from the partition decision maker 324, may performa re-partition operation and/or trigger one or more content updatesbetween the tiers 328 (e.g., between the top-tier (Tier 1) and thesecond tier (Tier 2). In some embodiments, a partitioner 330 of apartition manager system in accordance with example embodiments of thedisclosure may adjust the allocation of partitions of one or more tiers328 (e.g., a top-tier) in the storage pool for each client 303. Each ofthe clients 303 may access the one or more corresponding partitions ofone or more tiers 328 allocated by the partitioner 330.

Although some of the components illustrated in FIG. 3 may be shown asindividual components associated with other specific components, inother embodiments, components may be combined, split apart, and/orassociated with other components. For example, in some embodiments, thepartition decision maker 324 and partitioner 330 may be combined in asingle component located in the application server layer 304, thestorage layer 306, and/or some other location.

The partition manager interface 322 may enable a partition managersystem in accordance with example embodiments of the disclosure toprovide one or more interfaces and/or functions to clients 303, forexample, through an application programming interface (API).

When an I/O request from a client arrives at the application serverlayer 304, the hypervisor I/O filter (HIF) 320 may differentiate eachI/O stream and conduct a statistical analysis such as determining aworkload change and/or top-tier storage device cache hit ratio. The I/Orequest may then proceed to the partition manager interface 322 whichmay provide a standard I/O interface for various clients.

Algorithm 1 illustrates some example operations of an embodiment of aninterface that may provide file-oriented storage operations on thestorage layer 306 for a client 303 in accordance with exampleembodiments of the disclosure. When one of the functions illustrated inAlgorithm 1 is invoked, the return type provided by the algorithm may beindicted by the “=>” symbol.

FIG. 4 illustrates example embodiments of inputs and outputs for aninterface for file-oriented storage operations in accordance withexample embodiments of the disclosure. The embodiment illustrated inFIG. 4 may be used, for example, with the embodiment illustrated inAlgorithm 1. Each of the functions illustrated in FIG. 4 may be invokedwith the corresponding input. The function may then respond with thecorresponding output as shown in FIG. 4.

Algorithm 1  1 # File-oriented Storage  2 Interface PDMS_IO_API_FS:  3 Function CreateANewFile(pathToFile) => bool  4  FunctionOpenAnExistingFile(pathToFile) => pointerToFile or fileContent  5 Function ReadFileContents(pathToFile) => fileContent  6  FunctionSearchData0nAFile(pathToFile, data) => pointerToFile or bool  7 Function WriteIntoANewFile(pathToFile, data) => bool  8  FunctionUpdateContentsToAnExistingFile(pathToFile, offset, data) => bool  9 Function DeleteAFile(pathToFile) => bool 10  FunctionCloseAFile(pathToFile) => bool

Algorithm 2 illustrates some example operations of an embodiment of aninterface that may provide object-oriented storage operations on thestorage layer 306 for a client 303 in accordance with exampleembodiments of the disclosure. When one of the functions illustrated inAlgorithm 1 is invoked, the return type provided by the algorithm may beindicted by the “=>” symbol.

Algorithm 2  1 # Object-oriented Storage  2 Interface PDMS_IO_API_OBJ: 3  Function CreateANewObiect(key, value) => bool  4  FunctionOpenAnExistingObject(key) => key or value  5  FunctionReadObjectContents(key) => value  6  Function SearchDataOnAObject(key,value) => <key, value> or   <key, value, offset> or bool  7  FunctionWriteIntoANewObject(key, value) => bool  8  FunctionUpdateContentsToAnExistin Object(key, offset, value) => bool  9 Function DeleteA0bject(key) => bool 10  Function CloseA0bject(key) =>bool

FIG. 5 illustrates example embodiments of inputs and outputs for aninterface for object-oriented storage operations in accordance withexample embodiments of the disclosure. The embodiment illustrated inFIG. 5 may be used, for example, with the embodiment illustrated inAlgorithm 2. Each of the functions illustrated in FIG. 5 may be invokedwith the corresponding input. The function may then respond with thecorresponding output as shown in FIG. 5.

In the file-oriented embodiments illustrated in Algorithm 1 and FIG. 4,the interface may operate on a file (which may be pointed to by a pathto the file). In the object-oriented embodiments illustrated inAlgorithm 2 and FIG. 5, the interface may operate on key-value pairs(which may be pointed to by a key).

In some embodiments, a partition manager system in accordance withexample embodiments of the disclosure may adapt different storagesystems based, for example, on client requests. Moreover, depending onthe implementation details, the adaptation process may be transparent tothe cloud client layer 302 and/or the storage layer 306. In someembodiments, the partition manager interface 322 may be extended tosupport additional I/O storage types, for example, customized I/Ostorage types, based on client demand for the additional storage types.

After an I/O request passes through the partition manager interface 322,the partition decision maker 324 may analyze the behavior of eachclient's applications and corresponding feedback from one or more of thestorage tiers 328 (e.g., from the top-tier which may operate as astorage cache). In some embodiments, the partition decision maker 324may use this analysis and feedback to adjust each client's partition ofthe top-tier (Tier 1), for example, to improve or optimize the overallperformance of the entire storage system and/or ensure fairness based onfactors such as quality-of-service (QoS) and/or the actual workloadbehavior for each client. The partition decision maker 324 mayperiodically and/or dynamically adjust the storage partition size of oneor more of the tiers 328 (e.g., the top-tier which may be the highestperformance tier) for each client based on runtime workload analysisresults.

In some embodiments having two or more tiers of storage devices, thealgorithms and/or operations described herein may be implemented betweenmultiple pairs of tiers, for example, between Tier 1 and Tier 2, betweenTier 2 and Tier 3, between Tier 1 and Tier 3, and/or the like,

Table 1 illustrates some example implementation details of an exampleembodiment of an all SSD storage layer 306 in accordance with exampleembodiments of the disclosure. Each tier may be implemented with adifferent type of storage device that may different characteristicssuitable for that tier. The details illustrated in Table 1 may be used,for example, with the embodiment of a storage layer 306 illustrated inFIG. 3.

In some embodiments, some example values, parameters, and/or the likemay be provided for purposes of illustrating the principles, but theprinciples are not limited to these examples, and other values,parameters, and/or the like may be used.

TABLE 1 Read Write Tier Latency Latency ID Storage Device Characteristic(μs) (μs) Tier 1 Cross-grid, bulk Very High 10 μs  10 μs resistancechange performance Tier 2 SLC NVMe SSD High performance 25 μs  200 μsTier 3 MLC NVMe SSD Middle performance 50 μs 1400 μs Tier 4 TLC NVMe SSDLarge capacity 250 μs  2700 μs Tier 5 QLC NVMe SSD Large capacity 283μs  3000 μs

Referring to Table 1, Tier 1 may be implemented with storage devicesbased on persistent memory such as cross-gridded nonvolatile memory withbulk resistance change which may provide very high performance. Tier 1may operate, for example, as a storage cache for one or more of theother tiers. Tier 2 may be implemented with single-level cell (SLC) NVMeSSDs which may provide high performance but not as high as Tier 1. Tier3 may be implemented with multi-level cell (MLC) NVMe SSDs which mayprovide middle-level performance. Tiers 4 and 5 may be implemented withtriple-level cell (TLC) and quad-level (QLC) NVMe SSDs, respectively,which may provide successively lower performance but higher capacity.Such an embodiment may be used, for example, for cloud computingapplications. A partition manager system in accordance with exampleembodiments of the disclosure may adjust periodically and/or dynamicallyadjust each client's partition, for example, in the top-tier which mayoperate as a storage cache for a storage system such as a disaggregatedstorage system. In some embodiments, a partition manager system inaccordance with example embodiments of the disclosure may apply similaradjustment methods, for example, between Tier 2 and Tier 3, where Tier 2may operate as a cache tier for Tier 3, and so on.

FIG. 6 illustrates an example embodiment of a storage layer inaccordance with example embodiments of the disclosure. In the embodimentillustrated in FIG. 6, the storage layer 606 may be implemented tiers628 having a combination of SSDs and HDDs. Table 2 illustrates someexample implementation details that may be used, for example, with thestorage layer 606 illustrated in FIG. 6.

TABLE 2 Granularity Granularity Tier ID Type Usage example degreeexample Tier 1 SLC Caching game runtime data and Fine File or part ofhot game image (hot files) block Tier 2 QLC Hot game images (entiregame). Coarse Game Image Tier 3 HDD All game images (entire game).Coarse Game Image

Referring to Table 2, Tier 1 may be implemented with SLC NVMe SSDs whichmay provide a very high level of performance and a relatively fine levelof granularity. Tier 1 may operate, for example, as a storage cache forone or more of the other tiers. Tier 2 may be implemented with QLC NVMeSSDs which may provide a relatively high level of performance and arelatively coarse level of granularity. Tier 3 may be implemented withHDDs which may provide a relatively lower level of performance andrelatively coarse granularity, but at a relatively low cost.

The embodiment illustrated in FIG. 6 and Table, 2 may be used, forexample, for an online game streaming service datacenter. The top-tier(Tier 1) may be used to cache runtime game data such as a runtimeinstance of the game, metadata, the status of gameplay, all or part of ahot game image (e.g., hot files), and/or the like. Some embodiments mayuse a delta differential storage approach to further save space. Thesecond tier (Tier 2) may have a combination of relatively highperformance and relatively large capacity to cache hot game images.Thus, Tier 2 may operate as a cache for Tier 3. The third tier (Tier 3)may have a large capacity and may be used as a storehouse for gameimages (e.g., all game images).

2.3 Workflow Architecture

FIG. 7 illustrates an example embodiment of a workflow architecture fora partition manager system in accordance with example embodiments of thedisclosure. The embodiment illustrated in FIG. 7 may be used, forexample, on, with, in conjunction with, and/or the like, any of theembodiments disclosed herein, including the embodiments illustrated inFIGS. 1-6. For purposes of illustration, the embodiment illustrated inFIG. 7 may be described in the context of a system having a storagelayer with a top-tier that may operate as a storage cache for one ormore other tiers. However, the principles may be applied to any otherconfiguration of tiers and/or caches.

The embodiment illustrated in FIG. 7 may include a workload monitorsubsystem (Subsystem 1) 702, a burst detector subsystem (Subsystem 2)710, a strategy selector subsystem (Subsystem 3) 718, and a partitionoperator subsystem (Subsystem 4) 724. The workload monitor subsystem 702may include a workload status monitor (Component 1) 704 and a hit ratiomonitor component (Component 2) 706. The burst detector subsystem 710may include a burst degree calculator (Component 3) 714 and a burstdetector (Component 4) 716. The strategy selector subsystem 718 mayinclude an aggressive solution component (Component 5) 720 and anoptimal solution component (Component 6) 722. The partition operatorsubsystem 724 may include a partitioner component (Component 7) 726.

The workflow illustrated in FIG. 7 may operate in an overall loop toperiodically and/or dynamically adjust each client's storage partitionsize in one or more tiers of a storage layer. For example, the workflowmay adjust each client's storage partition size in a top-tier (e.g., thehighest performance tier in some implementations) based on runtimeworkload analysis results.

In some embodiments, the workflow illustrated in FIG. 7 may operate ontwo temporal windows running in parallel in a storage system. FIG. 8illustrates example embodiments of temporal windows for a workflow for apartition manager system in accordance with example embodiments of thedisclosure. As illustrated in FIG. 8, a first window (Window 1) mayoperate on relatively short cycles during which the workflow may monitorworkload behaviors and/or cache status information collected by theworkload monitor subsystem 702.

In some embodiments, Window 1 may be implemented as a performancemonitoring sliding window (PMSW) 708 in which workflow and/or cachestatus data may be sampled, collected, processed and/or the like over anepoch that may move with time. In some example implementations, Window 1may have an epoch length T1 of about 5 minutes, although any otherperiod of time may be used. In some embodiments, Window 1 may set afrequency at which the burst detector subsystem 710 may record workflowand/or cache status (e.g., to tier hit ratio) data collected by theworkload monitor subsystem 702. Examples of workload behaviors that maybe used by the burst detector subsystem 710 may include working set (WS)size in the most recent epoch, working volume (WV) size in the mostrecent epoch, read ratio (R) in the most recent epoch, and/or the like,which may be described in more detail below. In some embodiments, apartition manager system in accordance with example embodiments of thedisclosure may retain workflow and/or cache status data for the k mostrecent continuous or discrete epochs, where k may be any number. In someexample implementations, k may be 10. In some embodiments, anexponential moving average window (EMAW) technique may be applied to thedata for the k epochs.

In some embodiments, Window 2 may be implemented as a partitionadjustment and content update window (PACUW) 712. Window 2 may determinea re-partition period at which a new re-partition evaluation may betriggered. At a re-partition boundary, the burst degree calculatorcomponent 714 may be triggered by Window 2 to determine an approach forcalculation of a burst degree (Bd), which may indicate an impending I/Oburst based on the read ratio (R) which may be described in more detailbelow. In some embodiments, Window 2 may have a window length T2 thatmay be larger than one epoch of Window 1. For example, T2 may be aboutone hour, although any other period of time may be used. In someembodiments, implementing Window 2 longer than Window 1 may reduce thecost of operating a partition manager system because, depending on theimplementation details, re-partitioning may be relatively expensive interms of bandwidth, power consumption, and/or the like. In someembodiments, the relative lengths of Window 1 (T1) and Window 2 (T2) maybe selected to balance the tradeoff between performance and overhead.For example, re-partitioning more frequently may provide improvedperformance, but depending on the implementation details, the improvedperformance may be outweighed by the increase in overhead associatedwith re-partitioning. Between re-partitionings, the burst detectorsubsystem 710 may continue receiving working set size (WS), workingvolume size (WV), read ratio (R), and/or other data that may be gatheredby the workload monitor subsystem 702 during Window 1 epochs.

Table 3 lists some example embodiments of various aspects related to aworkflow for a partition manager system in accordance with exampleembodiments of the disclosure. Table 3 lists each aspect along with acorresponding symbol and a corresponding code symbol that may be used,for example, in one or more algorithms disclosed herein. In someembodiments, the aspects listed in Table 3 may be described as follows.

Working volume size |V| may indicate the total amount of data (e.g., inbytes) accessed on a storage device or other unit of storage resource.In memory-related contexts (e.g., dynamic random access memory (DRAM)),working volume size may be referred to as a footprint.

Working set size |S| may indicate a total address range (e.g., in bytes)of accessed data, which may be, for example, a set of working addressesfor a working volume. In some embodiments, a large working set may covermore storage space. If the cache size is larger than or equal to theworking set size for a workload, the I/O hit ratio of the workload maybe equal or close to 100 percent, for example, using a least recentlyused (LRU) caching algorithm.

Read ratio R may be determined, for example, by a read working volume bya total working volume, where the total working volume may be determinedby the sum of the read working volume and the write working volume. Insome embodiments, the range of the read ratio may be zero to one-hundredpercent [0%, 100%] where a higher read ratio may indicate a moreread-intensive workload.

Window 1 W₁ (e.g., the length of the PMSW) may indicate the epoch lengthT1 during which workload behaviors and/or cache status information maybe recorded before beginning a monitoring cycle.

Window 2 |W₂| (e.g., the length of the PACUW) may indicate the period T2of re-partition. This window may trigger an entire re-partitionoperation workflow from the burst detector subsystem 710, through thestrategy selector subsystem 718, and to the partition operator subsystem724.

TABLE 3 Aspect Code Symbol Symbol Working Volume Size WV |V| Working SetSize WS |S| Read Ratio R R Epoch for PMSW W1 W₁ PACUW W2 W₂

Referring again to FIG. 7, at intervals that may be determined by Window2, the burst detector subsystem 710 may calculate a burst degree based,for example, on a recently determined different read ratio (R). (In someembodiments, a burst may also be referred to as a spike.) The burstdegree calculation may be performed, for example, by the burst degreecalculator 714. For read-intensive workloads (as determined, forexample, based on the read ratio (R), the burst degree may be calculatedbased on a working set (WS) size change. For non-read-intensiveworkloads, the burst degree may be calculated based on a working volume(WV) and/or footprint size change.

After the burst degree calculator 714 determines the burst degree, itmay transfer this information to the burst detector 716, which maycompare the burst degree to a preset threshold to determine whether thecurrent workload may be characterized as bursty or non-bursty. Thebursty/non-bursty determination may be used to determine which type ofre-partitioning strategy to use in the strategy selector subsystem 718.

If the current workload is bursty, the workflow illustrated in FIG. 7may invoke the aggressive solution component 720 to apply an aggressivere-partitioning strategy which may adjust the top-tier partition foreach client proportionally, for example, based on demands during one ormore recent PMSW epochs. For example, an aggressive approach may adjustthe partition of each client based on its recent working set size change(for read-intensive workloads) or working volume size change (fornon-read-intensive workloads). In some embodiments, an aggressivestrategy may be implemented relatively quickly, which may enable thesystem to react quickly to accommodate an impending expected I/O burst.

However, if the current workload is non-bursty, the system may havesufficient time to apply an optimization framework using the optimalsolution component 722, which may strive to find a global best partitionsolution, for example, to best utilize the top-tier (e.g., cache tier)by solving, improving and/or maximize an objective function as describedbelow. Thus, for a non-bursty workload, the optimal solution component722 may be selected to apply a re-partitioning strategy based on anoptimization framework which may consider different factors relating toall of the hosting clients such as the workload change in one or morerecent PMSW epochs, the estimated hit ratio if the partition size isincreased or decreased, the weight of each client based, for example, onquality-of-service (QoS) and/or service level agreements (SLAs), and/orthe like.

The partitioner component 726 may conduct the actual re-partitioningoperation, for example, on a top-tier of a storage level, based on theresulting partition strategy provided by the strategy selector subsystem718. The workflow illustrated in FIG. 7 may then loop back to waitingfor the next re-partitioning operation to be triggered by Window 2 inthe burst detector subsystem 710.

3. Burst Detection

A burst detector subsystem 710 in accordance with example embodiments ofthe disclosure may detect whether the current workload of a storagelayer may be bursty or non-bursty to enable a strategy selectorsubsystem 718 to select the re-partitioning strategy base on a burstdegree, since a higher burst degree may allow less time to react, andvice versa. In some embodiments, a burst (which may also be referred toas a spike) may be characterized by a relatively high number of I/Oaccesses on a relatively large amount of data that may occur within arelatively short period of time.

In some embodiments, a burst detection operation may take intoconsideration the I/O patterns of all or most clients, for example, allI/O client accesses of the storage layer in one or more recent PMSWepochs, to determine which strategy to use for re-partitioning. In someother embodiments, however, a burst status determination may focus on arelatively small number of clients (e.g., on a per client basis).

In some embodiments, a burst degree calculation may involve differentapproaches based on the read ratio (R) of recent access of all or mostclients to the top-tier storage. For example, a preset read ratiothreshold a may be used to determine whether a recent workload isread-intensive or non-read-intensive. For purposes of illustration, emay be set to 95 percent in some example embodiments disclosed herein.However, in other implementations, e may be set to any suitable valuefor determining a threshold for a read-intensive workload, for example,in the range of [0%, 100%].

In some embodiments, if the read ratio is in the range [0, e), theworkload may be classified as non-read-intensive. In this case, a changein the size of the working volume may be used to calculate the burstdegree. In some embodiments, the working volume change (which may alsobe referred to as a footprint), may include the entire record of alltouched addresses. For non-read-intensive workloads, the working volumemay be used to calculate the burst degree because, if there are arelatively large number of write I/Os, each new write request may beassigned to a new slot, and repeated write requests for the same addressmay also be assigned new slots in the cache. Thus, the burst degreecalculation may be based on the change in the working volume size.

FIG. 9 illustrates an example embodiment of I/O requests for anon-read-intensive workload in accordance with example embodiments ofthe disclosure. In the embodiment illustrated in FIG. 9, a top-tier(e.g., storage cache) 902 may be shown at times T0 through T5. The table904 may indicate the read or write operation performed on the datachunks A, B, C, and D at each time and the amount of data in each chunk.Letters may indicate the chunks of data, and letters with tick marks(e.g., C′) may indicate updated data. At times T0-T3, data A, B, C, andD may be written to the top-tier 902. At time T4, the two A chunks andtwo of the B chunks may be evicted and overwritten by the C′ data. Attime T5, one of the D chunks may be read from the top-tier 902. Thus,the storage system may assign new slots for each new write request, andrepeated write requests of the same address may also be assigned newslots in the cache (e.g., the four new chunks of data C at time T4).Thus, the system may base the burst degree calculation on the change inthe size of the working volume of the workload.

Algorithm 3 illustrates some example operations of an embodiment of aburst degree calculation in accordance with example embodiments of thedisclosure. Algorithm 3 may be performed, for example, by the burstdegree calculator component 714 (Component 3 of Subsystem 2) illustratedin FIG. 7). In the embodiment illustrated in Algorithm 3, code for theparameter selection for a non-read-intensive case may be located atlines 4-7.

Algorithm 3  1 Subsystem_2_Burst_Detector:  2 Component_3_Burst_Degree_Cacluator:  3   preset threshold e=95%  4  Function calBurst( ):  5    if writePercentage in [0, e):  6     #non-read-intensive workload  7     burstDegree=calBurst(curWV, preWV)  8   else if readRatio in [e, 1]:  9     # read-intensive workload 10    burstDegree=calBurst(curWS, preWS) 11   Function calBurst(cur, pre):12    return |cur-pre|/|cur| 13  Component_4_Burst_Detector: 14   presetthreshold bt=0.5 15   Function burstFlag( ): 16    if burstDegree>0.5:17     return True 18    else: 19     return False

In some embodiments, if the read ratio is in the range [e, 1], theworkload may be classified as read-intensive. In this case, a change inthe size of the working set may be used to calculate the burst degree.In some embodiments, the working set may be characterized as adeduplicated version of the working volume.

FIG. 10 illustrates an example embodiment of I/O requests for aread-intensive workload in accordance with example embodiments of thedisclosure. In the embodiment illustrated in FIG. 10, a top-tier (e.g.,storage cache) 1002 may be shown at times T0 through T5. The table 1004may indicate the read or write operation performed on the data chunks A,B, C, and D at each time and the amount of data in each chunk. At timesT0-T3, data chunks A, B, C, and D may be read from the top-tier 1002. Attime T4, data chunk C may be read again. At time T5, data chunk D may beread again. As illustrated in FIG. 10, with a read-intensive workload,the system may not assign a new slot for repeated I/O requests if therequested I/O content has already been cached in the top tier 1002 (andis still present in the cache). Thus, the system may base the burstdegree calculation on the change in the size of the working set of theworkload (e.g., the unique addresses that have been touched).

In the embodiment illustrated in Algorithm 3, code for the parameterselection for a read-intensive case may be located at lines 8-10.

Once the parameter (e.g., working volume size or working set size) hasbeen selected to use for the burst calculation, it may be used tocalculate the burst degree. In some embodiments, a piecewise functionmay be used to calculate the burst degree, for example, as shown inEq. 1. Some of the symbols used in Eq. 1 may be characterized asfollows.

|V_(curwin)| may represent the working volume size of the current PMSWepoch.|V_(prevwin)| may represent the working volume size of the previous PMSWepoch.|S_(curwin)| may represent the working set size of the current PMSWepoch.|S_(prevwin)| may represent the working set size of the current PMSWepoch.The delta function may be used to track changes in the working set(Δ(S_(curwin), S_(prevwin)))

or working volume sizes (Δ(V_(curwin), V_(prevwin))) between the currentand previous PMSW windows. (In some embodiments, the same method may beused to consider more than two PMSW windows to calculate burst degree.)The relative difference between the two PMSW windows may then becalculated as the burst degree Bd as follows:

$\begin{matrix}{B_{d} = \left\{ \begin{matrix}{{{\Delta\left( {V_{curwin},V_{prevwin}} \right)} = \frac{{v_{curwin}} - {v_{prevwin}}}{v_{curwin}}},} & {{{if}\mspace{14mu} R} \in \left\lbrack {0,e} \right)} \\{{{\Delta\left( {S_{curwin},S_{prevwin}} \right)} = \frac{{s_{curwin}} - {s_{prevwin}}}{s_{curwin}}},} & {{{if}\mspace{14mu} R} \in \left\lbrack {e,1} \right\rbrack}\end{matrix} \right.} & {{Eq}.\mspace{14mu} 1}\end{matrix}$

The calculated value of Bd may then be compared to the predefined burstthreshold Bt. If the Bd>Bt, it may indicate that the current workloadmay be characterized as bursty. The value of Bt may preset to anysuitable value, for example, in the range of 40 to 60 percent. In someembodiments, setting the value of Bt to 50 percent may ensure that thebeginning (ascending edge) and ending (descending edge) of a burst maybe captured. For example, if Bt is set to 50 percent, it may indicatethat if a change of more than 50 percent of the working volume sizechange (for non-read-intensive case) or working set size change (forread-intensive case) is detected, the workload is determined to bebursty.

In some embodiments, some conditional relationships and supportingconsiderations for a burst degree calculator component such as Component3 illustrated in FIG. 7 may be as follows. For a read-intensiveworkload, the burst degree calculation may be based on a change in theworking set size of the current workload. For read-intensive workloads,the storage system may not assign a new slot in a top-tier (e.g., astorage cache) for repeated I/O requests if the requested I/O contenthas already been cached in the cache (and is still in the cache). Thus,the burst degree calculation may be based on a change in the working set(which may include unique addresses that have been touched).

For non-read-intensive workloads, the burst degree calculation may bebased on a change in the working volume size of the current workload. Ifthe workload includes a relatively large number of write I/Os, new slotsmay be assigned in a top tier for each new write request, and repeatedwrite requests of the same address may also be assigned new slots in thecache. Thus, the burst degree calculation may be based on a change inthe working volume of the workload. In some embodiments, the workingvolume may be a footprint which may include the entire record of alltouched addresses. Thus, a working set may be characterized as adeduplicated version of the working volume.

In some embodiments, some conditional relationships and supportingconsiderations for a burst detector component such as Component 4illustrated in FIG. 7 may be as follows. For a bursty workload, solvingan optimization framework may take more time than may be availablebefore a burst arrives. Therefore, an aggressive approach may be appliedto a re-partitioning operation. In some embodiments, an aggressiveapproach may adjust the partition of each client based on a recentchange in its working set size (for a read-intensive workload) orworking volume (for a non-read-intensive. workload). For a non-burstyworkload, a partition manager system may have sufficient time to solvean optimization framework. Therefore, an optimized approach, which maystrive to find a global best partition solution to achieve the bestobjective function, may be applied to a re-partitioning operation.

FIG. 11 illustrates an example embodiment of a burst calculation andburst detection method in accordance with example embodiments of thedisclosure. The method may begin at operation 1102 where the read ratiofor the current workload may be compared to the read ratio threshold e.If the read ratio is less than or equal to e, the method may proceed tooperation 1104 where the change in working set may be used to calculatethe burst degree Bd. However, if at operation 1102 the read ratio isdetermined to be greater than e, the method may proceed to operation1106 where the change in working volume may be used to calculate theburst degree Bd. At operation 1108, the burst degree Bd may be comparedto the burst threshold Bt. If the burst degree is greater than Bt, themethod may proceed to operation 1112 where the current workload isdetermined to be a bursty workload. However, if at operation 1110 theburst degree is less than or equal to Bt, the method may proceed tooperation 1114 where the current workload is determined to be anon-bursty workload.

4. Partitioning Methodology for Bursty Workloads

When bursty I/Os are identified by a burst detector such as the burstdetector subsystem 710, a partition manager system in accordance withexample embodiments of the disclosure may aggressively adjust thepartition for each client in a tier of storage (e.g., a top-tier whichmay operate as a storage cache) based on a recent change in its workingset size (for read-intensive workloads) or working volume size (fornon-read-intensive workloads). In some embodiments, this may result in arelatively fast re-partitioning operation that may accommodate animpending I/O burst.

4.1 Partitioning Workflow for Bursty Workloads

In some embodiments, a partitioning method for a bursty workload inaccordance with example embodiments of the disclosure may determine apartition size for each client based, at least in part, on one or moreof the following two aspects of the workload: (1) a workload changeduring a recent epoch (e.g., of the PMSW); and/or (2) a hit ratio for acache in a current epoch.

Although not limited to any specific implementation details, thepartitioning method for a bursty workload described below may be used,for example, by the aggressive solution component 720 of the strategyselector subsystem 718 based on feedback about the workload, forexample, data received from the workload monitor subsystem 702illustrated in FIG. 7.

In some embodiments, the workload change may be used to calculate ademanded space size (DSS), for example, to quickly adapt to workloadchanges. For example, a client may experience an I/O burst which mayinvolve a relatively large amount of cache space. However, if adequatespace for the I/O burst is not available in the cache, it may increasethe delay and/or latency for that client. In some embodiments, a DSS maybe used to reduce or prevent this type of situation.

In some embodiments, the storge cache hit ratio may be used to calculatea guaranteed minimal space size (GMSS), for example, as a contributionratio of the cache for each client. In some embodiments, this may beused to reduce or prevent the cached slot from being flushed from thecache caused by I/O bursts by other clients.

FIG. 12 illustrates an example embodiment of a method for a partitioningmethod for a bursty workload in accordance with example embodiments ofthe disclosure. The method illustrated in FIG. 12 may be performed, forexample, by the aggressive solution component 720 illustrated in FIG. 7.The method may begin at operation 1202 where the current epoch status(lines 3-4) may be obtained from the PACUW window 712 which may recordmultiple epoch information from the PMSW window 708 in the workloadmonitor subsystem 702. At operation 1204, a workload amount for eachclient may be calculated as described below. At operations 1206 and1208, a cache upperbound and lowerbound may be calculated, respectivelyfor each client based on the workload amount as described below. Atoperation 1210, a client list may be sorted based on the workload amountand a weight for each client which, in some embodiments may be based ona QoS. At operation 1212, the cache may be partitioned to each clientone-by-one to satisfy each client's upperbound such that partitions forclients with a higher weight (e.g., priority) may be allocated first. Atoperation 1214, the partitioning plan may be sent to the partitionoperation subsystem 724 for implementation.

Any type of weight function may be used for the sorting and/orpartitioning operations. In some embodiments, any weight function may beused to combine a workload amount and a QoS. In some exampleimplementations, a percentage-based QoS may be multiplied with aworkload amount. For example, for client i, with workload amount Wi andQoS percentage Qi, a weighted workload amount may be calculated as

$\begin{matrix}{{w_{i} = {\frac{Q_{i}}{\sum_{v \in V}Q_{v}} \times W_{i}}},} & {{Eq}.\mspace{14mu} 2}\end{matrix}$

where v may be the iterated client in the set of all clients V.

Algorithm 4 illustrates some example operations of an embodiment of amethod for a partitioning method for a bursty workload in accordancewith example embodiments of the disclosure. Algorithm 4 may beperformed, for example, by the aggressive solution component 720illustrated in FIG. 7. In the embodiment illustrated in Algorithm 4,code to obtain the current epoch status may be located at lines 3-4.

Algorithm 4  1 Subsystem_3_Stradegy_Selector:  2 Component_5_Aggressive_Solution:  3   # Step 1: Get current epochstatus  4   curEpochStatus=getCurEpochStatus( )  5   # Step 2: Calculateworkload amount  6   workloadAmountList = for each clientID,calWorkloadAmount(clientID,    curEpochStatus)  7   # Step 3: Calculatecache upperbound of each client  8   upperboundList . for each clientID,calUpperbound(clientID,    curEpochStatus)  9   # Step 4: Calculatecache lowerbound of each client 10   lowerboundList = for each clientID,calLowerbound(clientID,    curEpochStatus) 11   for clientID inlowerboundList: 12    if lowerbound(clientID) >= upperbound(clientID):13     lowerbound(clientID) = upperbound(clientID) 14   # Step 5: Sortclients by workload amount + QoS 15  sortedClientList=sortBy(workloadAmountList, OoSList) 16   # Step 6:Satisfy client's upperbound one-by-one, higher priority    clients gofirst 17   plan = for client in sortedClientList:satisfy(upperboundList,    lowerboundList) 18   # Step 7: Send plan tosubsystem 4 19   return plan

4.2 Workload Amount

A workload amount |W| may be used to represent an actual workloadamount, for example, from the perspective of a cache slot allocation. Insome embodiments, the workload amount may be determined by a piecewisefunction based on different workload read ratios as shown in Eq. 3.

$\begin{matrix}{{W}_{i} = \left\{ \begin{matrix}{{{V}_{i},}\ } & {{{íf}\mspace{14mu} R} \in \left\lbrack {0,e} \right)} \\{{{S}_{i},}\ } & {{{íf}\mspace{14mu} R} \in \left\lbrack {e,1} \right\rbrack}\end{matrix} \right.} & {{Eq}.\mspace{14mu} 3}\end{matrix}$

In some embodiments, read-intensive workloads new cache slots may not beallocated for repeatedly requested addresses because they may not modifythe content. Thus, as shown in Eq. 3, if the recent PMSW epoch workloadis a non-read-intensive workload, then the working volume may be used asthe workload amount. However, if the recent PMSW epoch workload is aread-intensive workload, then the working set may be used as theworkload amount.

At the end of each PMSW epoch, a partition management system inaccordance with example embodiments of the disclosure may check therecent status of all clients sharing the disaggregated storage system.Table 4 illustrates some example values of status information that maybe obtained from the workload monitor subsystem 702 and recorded by thePACUW window 712 in the burst detector subsystem 710. The valuesprovided in Table 4 are for purposes of illustration only, and othervalues may be obtained and/or used.

As illustrated in Table 4, the working set size |S| or the workingvolume size |V| may be selected as the workload amount |W| which may beused to calculate the next epoch allocation.

TABLE 4 |V| |S| (Working H R (Working Volume |W| |C| (Hit (Read Set Size(Workload (Cache Ratio Client Ratio in Size in Size in Amount in Size inin ID Recent Recent Recent Recent Recent Recent (i) Epoch) Epoch) Epoch)Epoch) Epoch) Epoch) Client 1 97% 100 GB  760 GB  100 GB  40 GB 35%Client 2 78% 120 GB  200 GB  200 GB  60 GB 70% Client 3 47%  30 GB 1430GB 1430 GB 100 GB 43% Client 4 98%  10 GB  66 GB  10 GB  50 GB 29%

In some embodiments, the status information may include additionalinformation such as touched the number, touched file part vs touched thesize percentage, and/or the like.

4.3 Upperbound and Lowerbound

For a bursty workload, a partition management system in accordance withexample embodiments of the disclosure may aggressively and/orproportionally assign top-tier storage resources (which may operate ascache space) to each client based on the client's workload amount forthe recent epoch. Thus, the system may attempt to dynamically and/oraggressively assign more top-tier storage resources to clients that mayhave more bursty I/Os in the recent epoch. In some embodiments, thesystem may strive to aggressively push each client's next epoch cachespace to its demand based on the current epoch status of the client. Toachieve this allocation, cache space may be proportionally reallocatedamong all clients using the upperbound as set forth in Eq. 4.

$\begin{matrix}\left\{ \begin{matrix}{{{Upperbound}\text{:}\mspace{14mu}{C}_{new}(i)} = {\frac{{W}_{i}}{\Sigma_{i \in {\{ V\}}}{W}_{i}} \times {C}_{\max}}} \\{{{Lowerbound}\text{:}\mspace{14mu}{C}_{new}(i)} = {{C}_{cur}(i)\  \times {H}_{cur}(i)}}\end{matrix} \right. & {{Eq}.\mspace{14mu} 4}\end{matrix}$

In some embodiments, the upperbound may be referred to as demanded spacesize (DSS), for example, because it may be close to or match the sizefor the next epoch based on a proportional allocation method.

In some embodiments, the lowerbound may be used to ensure that one ormore clients may have a guaranteed minimum space size (GMSS), forexample, so that their cached data may not be easily flushed due tobursts in the workload. For example, based on the last epoch's hit rate,the last hit percent of the caches may potentially he useful in the nextepoch. Thus, that amount may be used as the minimal guaranteed cachespace for each client.

Code to obtain the upperbounds and lowerbounds for each client may belocated at lines 7-10 of Algorithm 4.

In some embodiments, there may be a special case if the lowerbound isgreater than or equal to the upperbound, in which case the system mayassign the minimum value of the upperbound and the lowerbound to boththe upperbound and the lowerbound. That is, upperbound=min(lowerbound,upperbound) and lowerbound=min(lowerbound, upperbound). This may occur,for example, when a client's current epoch has a relatively high numberof cache hits (e.g., the lowerbound may be larger), while the workloadis not considered to be bursty in current epoch (e.g., the upperboundmay be smaller). In this case, the upperbound may be given greaterinfluence on the partition amount because it may be the target based onthe prediction. Therefore, the DSS may override any existing GMSS. (Insome embodiments, GMSS may be intended to prevent a client's cached datafrom being entirely flushed out due to bursts from other clients). Thismay be seen, for example, in lines 11-13 of Algorithm 4.

5. Partitioning Methodology for Non-Bursty Workloads

In some embodiments, for a non-bursty workload, a partition managersystem in accordance with example embodiments of the disclosure may haveadequate time to perform a more extensively optimized re-partitioningwhich may take into consideration one or more factors such as estimatedhit ratios, workloads, the weights of each client, and/or the like.

5.1 Partitioning Workflow for Non-Bursty Workloads

In some embodiments, a re-partitioning workflow for a non-burstyworkload in accordance with example embodiments of the disclosure mayadjust the partition size of each client (v) so as to maximize anobjective function which may provide a way to evaluate the effectivenessof a given partitioning plan.

Eq. 5 provides an embodiment of an optimization framework which may heused, for example, to re-partition one or more tiers (e.g., a top-tierwhich may operate as a storage cache) of a storage layer. Table 5provides some example meanings of symbols used in Eq. 5. Although theembodiment of the workflow illustrated in Eq. 5 is not limited to anyparticular implementation details, in some embodiments it may beimplemented, for example, by the optimal solution component 722illustrated in FIG. 7.

TABLE 5 Symbol Meaning |C|_(max) Total capacity of the first tier (cachetier). |C|_(v), |C|_(cur)(v) Both may represent the current cache sizeof client v. Δ|C|_(v) Discrete change (step) of cache of client v whichmay be iterated from [−|C|_(v), |C|_(max) − |C|_(v)]. The cache size ofclient v may be iterated from 0 to the entire capacity of the first tierstorage. A customized upperbound or lowerbound of each client's cachesize may be added by changing the range of Δ|C|_(v). w_(v) Weight ofclient v based on QoS, SLA, and/or the like. One implementation may be$w_{i} = {\frac{Q_{i}}{\Sigma_{v\;\epsilon\; V}Q_{v}} \times {W_{i}.}}$v, {V} One client v, and the all client set {V} ExpHitRatio(v, Expectedhit ratio of client v in the next epoch |C|_(v) + Δ|C|_(v)) if thechange of Δ|C|_(v) is added to the current cache size. ExpWorkVol(v)Expected working volume of client v in the next epoch. Δ|C|_(opt)(v),{Δ|C|_(opt) Under an optimal solution, the cache change size (v ∈ {V})}of client v, and the set of the cache change sizes of all clients,respectively. |C|_(new)(v) New size of client v's cache.

$\begin{matrix}{\left. {{{Max}\text{:}\mspace{14mu}\frac{1}{{C}_{\max}}{\sum\limits_{v \in {\{ V\}}}\left\lbrack {w_{v} \times {{ExpHitRatio}\left( {v,{{C}_{v} + {\Delta{C}_{v}}}} \right)} \times {{ExpWorkVol}(v)}} \right\rbrack}}\mspace{79mu}{\left. {{{S.t.\text{:}}\mspace{14mu}\Delta{C}_{v}} \in {{ - }C}} \right|_{v},{{C}_{\max} - {C}_{v}}}} \right\rbrack\mspace{79mu}{{{ExpHitRatio}\left( {v,{{C}_{v} + {\Delta{C}_{v}}}} \right)} \in \left\lbrack {{0\%},{100\%}} \right\rbrack}\mspace{20mu}{{\sum\limits_{v \in {\{ V\}}}\left( {\Delta{C}_{v}} \right)} = 0}\mspace{20mu}{{\sum\limits_{v \in {\{ V\}}}\left( w_{v} \right)} = {100\%}}} & {{Eq}.\mspace{14mu} 5}\end{matrix}$

The framework of Eq. 5 may begin by calculating the weighted sum of theexpected hit ratio of each client if the client has a cache size changeΔ|C|_(v) (e.g., ExpHitRatio(v, |C|_(v)+Δ|C|_(v))) multiplied by itsexpected working volume (e.g., ExpWorkVol(v) in the next PMSW epoch. Asmentioned above in section 4.1, the term “weight” (W_(v)) may reflecteach client's QoS, SLA, and/or the like. The term Δ|C|_(v) may beiterated for a range of possible cache assignment cases. In someembodiments, granularity of the iteration steps may be set to arelatively coarse-grained amount (e.g., 100 MB) which may reduce theoverhead associated with solving the optimization framework.

The framework of Eq. 5 may then divide the weighted sum by the totalcache size (|C|_(max)).

In some embodiments, a physical meaning of this result may becharacterized as the expected hit amount (e.g., a working volume, inbytes), expressed per-byte of cache capacity, that can be achieved inthe next epoch based on implementing a certain partition plan. Thus,maximizing the objective function of Eq. 5 may improve or optimize thepartitioning plan.

In some embodiments, the expected hit amount may be the total ofΔ|C|_(v) for all clients (that is, the Δ|C|_(v) list).

Eq. 5 may include a constraint section (“S.t.”), which may apply thefollowing limits: (1) the size of each client's space in the top tierstorage (e.g., cache size); (2) the range of expected hit ratio in [0%,100%]; (3) all change's (Δ|C|_(v)) sum to be zero (because the amount ofcache space may not change, it may only be reallocated between clients);and (4) the sum of all clients' weights to 100%.

In some embodiments, the objective function in Eq. 5 may be used to finda list of deltas (e.g., change of top tier storage amount) for allclients (wherein the list may be denoted {Δ|C|_(opt)(v∈{V})}) for anoptimal solution. Based on the list {Δ|C|_(opt)(v∈{V})}, a partitionmanager system in accordance with example embodiments of the disclosuremay return a final re-partition plan for all clients as shown in Eq. 6.

∀v∈{V}:|C| _(new)(v)=|C| _(cur)(v)+Δ|C| _(opt)(v)  Eq. 6

5.2 Hit Ratio Estimation

In some embodiments, to estimate the hit ratio (ExpHitRatio(v,|C|_(v)+Δ|C|_(v))), a reaccess distance-based analytical modelingframework may be used to provide online prediction of cache performancefor a range of cache configurations and/or replacement policies (e.g.,least recently used (LRU)).

An example embodiment of a reaccess distance-based analytical modelingframework in accordance with example embodiments of the disclosure isillustrated in Algorithm 5. A main procedure, which may be located atlines 1-6, may call the function CDF.update (where CDF may indicatecumulative distribution function) to update a CDF curve (which may beimplemented at lines 8-12). Based on the latest CDF curve, the hit ratiomay be estimated by inputting a given cache size to the getProbabilityfunction of CDF (which may be implemented at line 6). In someembodiments, this may determine how many percentages of the recordedaccessed data may have a reuse distance less than cacheSize.

The function runtimeUpdateRecordTable (which may be implemented at lines14-37) may be a separate function running in the background that mayupdate the record table when a new I/O request arrives.

Algorithm 5  1 Function estimateHitRatio(clientID, cacheSize):  2   #update CDF record  3   CDF.update(clientID, getEpochID( ), k)  4   #input: cacheSize as x-axis, we need to convert the unit  5   # output:probability (y-axis) of buckets having equal or less max    reaccessdistance than the cache size  6   returnCDF.getProbability(convertIOReqSizeToBucketsSize(cacheSize))  7  8 Function CDF.update(clientID, curEpochID, k):  9   # only focus onrecent k (preset number) epochs entries 10  focusTable=recordTable[clientID].filter(volume=“epochID”, rule=“>K”)11   # build a CDF data strucutre, x-axis is max reaccess distance, and   y-axis is the probability 12   buildCDF(focusTable.maxReuseDistance)13 14  Function runtimeUpdateRecordTable(clientID): 15   for each IOReqin clientID: 16    buckets=convertIOReqToBuckets(IOReq) 17    forbucketID in buckets: 18     curAccessTime+=1 19    recordEntry=recordHashTable[clientID][bucketID] 20     # no recordfound, then create a new entry 21     if (recordEntry==NULL): 22     recordEntry.setLastAccessTime(curAccessTime) 23     recordEntry.setEpochID(getEpochID( )) 24     recordEntry.setMaxReuseDistance(infinite) 25     recordHashTable[clientID][bucketID]=recordEntry 26     # foundrecord, then update it 27     else: 28     recordEntry.setLastAccessTime(curAccessTime) 29      if|recordEntry.getEpochID( )-getEpochID( )|<=k: 30       ifrecordEntry.getMaxReuseDistance( )==infinite: 32       recordEntry.setMaxReuseDistance(curAccessTime-       recordEntry.getLastAccessTime( )) 33       else: 34        #update ARD 35        recordEntry.setMaxReuseDistance(max(recordEntry.       getMaxReuseDistance( ),curAccessTime-recordEntry.       getLastAccessTime( ))) 36      else: 37      recordEntry.setMaxReuseDistance(infinite) 38     recordEntry.setEpochID(getEpochID( ))

In Algorithm 5, the function runtimeUpdateRecordTable(clientID) may runin the background during runtime. It may first convert incoming I/Orequests (from clientID) to data buckets which may have a granularityset, for example, to 5 MB or 50 MB for statistical analysis purposes. Acounter named curAccessTime may self-add 1 for each new data bucket.

Algorithm 5 may record the “distance” between the incoming I/O requestdata bucket's current access and its last access. In some embodiments,the distance may refer to the Absolute Re-access Distance (ARD)”, ratherthan Unique Re-access Distance (URD)”,

This may be understood with reference to a Re-access Interval (RI). Anaddress trace T may be a mapping of consecutive integers in increasingorder, representing successive positions in the trace. Tuples (x, τ) maybe used to represent all accesses where (x, τ)∈T, and where x mayrepresent the address and τ may identify its repetition number. Thefirst occurrence of address x in the trace may be represented by (x, 0).The expression t=T⁻¹ may denote the inverse function, and t(x, τ) maydenote the position of the τ-th occurrence of address X in the trace.

RI may be defined only when m>0 and may denote the portion of the traceenclosed between the m-th and (m−1)-th occurrence of x, as shown in Eq.7.

$\begin{matrix}{{{RI}\left( {x,\tau} \right)} = \left\{ \begin{matrix}{\left\{ \left( {\theta,\tau^{\prime}} \right) \middle| {{t\left( {x,{\tau - 1}} \right)} < {t\left( {\theta,\tau^{\prime}} \right)} < \left( {\theta,\ \tau} \right)} \right\},} & {{{if}\mspace{14mu}\tau} > 0} \\{{undefined},} & {else}\end{matrix} \right.} & {{Eq}.\mspace{11mu} 7}\end{matrix}$

The URD may then be calculated as shown in Eq. 8. RI may denote thetotal number of unique addresses between two occurrences of the sameaddress in the trace.

$\begin{matrix}{{{URD}\left( {x,\tau} \right)} = \left\{ \begin{matrix}{\left\{ \theta \middle| {\left( {\theta,\tau^{\prime}} \right) \in {{RI}\left( {x,\tau} \right)}} \right\},} & {{{if}\mspace{14mu}\tau} > 0} \\{{undefined},} & {else}\end{matrix} \right.} & {{Eq}.\mspace{14mu} 8}\end{matrix}$

ARD may also be calculated as shown in Eq. 9. ARD may denote the totalnumber of positions between two occurrences of the same address in thetrace.

$\begin{matrix}{{{ARD}\left( {x,\tau} \right)} = \left\{ \begin{matrix}{{{{{RI}\left( {x,\tau} \right)}} = {{t\left( {x,\tau} \right)} - {t\left( {x,{\tau - 1}} \right)} - 1}},} & {{{if}\mspace{14mu}\tau} > 0} \\{\infty,} & {else}\end{matrix} \right.} & {{Eq}.\mspace{14mu} 9}\end{matrix}$

The function may then search each new bucket in the recordTable, whichmay be implemented, for example, by a hash table where the key may bethe bucketID, and the value may be a tuple of multiple factors. If anentry is not found, it may indicate that this is the first time thisdata bucket has occurred, so a new entry may be created with values forthe entry saved in the recordTable. In some embodiments, the currentepochID may also be stored in the table too, for example, to furtherhelp fade out old data. Code for this operation may be located at lines10-29 of Algorithm 5.

Table 6 illustrates some example values that may be recorded in arecordTable by the function runtimeUpdateRecordTable(clientID). Thevalues provided in Table 6 are for purposes of illustration only, andother values may be obtained and/or used.

TABLE 6 (key) (value) bucketID lastAccessTime epochID maxReuseDistance00000001 0 0 1233 00000022 14176 4 464 00000510 6586 1 342 00001492 4350 53 . . .

In Algorithm 5, the function estimateHitRatio may be called to estimatethe cache hit ratio for a given cache size. The functionestimateHitRatio may trigger the function CDF.update which may updatethe CDF record, for example by building a new CDF curve of max-reusedistance and percentage of bins as shown in FIG. 13.

FIG. 13 illustrates an example embodiment of a CDF curve for a hit ratioestimation operation in accordance with example embodiments of thedisclosure. The CDF curve illustrated in FIG. 13 may help estimate thehit ratio given clientID and cacheSize. In FIG. 13, the X-axis mayrepresent the max-reuse distance, and the Y-axis may represent thepercentage of the number of buckets that have lower max-reaccessdistances than a certain distance in the X-axis. Thus, a hit ratioestimation operation may iterate different cache sizes (max-reusedistances) to check the upper bound of the hit ratio it can offer forthis period of workload. In some embodiments, a cache hit may bepossible only when the cache size is larger than the max-reuse distance.Thus, a connection may be built between the cache size and thetheoretical best result of an LRU caching algorithm hit ratio. In someembodiments, the curve may represent a maximum cache hit ratio. Thus, areduction adjustment may be assigned to it.

5.3 Working Volume Estimation

In some embodiments, an averaging technique may be used to estimate theworking volume ExpWorkVol(v). For example, some embodiments may use amoving window average technique such as a weighted moving average (WMA)and/or an exponentially weighted moving average (EWMA) to predict aworking volume. In some embodiments, a weighted average may beimplemented as an average having multiplying factors to give differentweights to data at different positions in a sample window. Thus,mathematically, a weighted moving average may be a convolution of datumpoints with a fixed weighting function. In some embodiments, an EWMAtechnique may involve weights that decrease in an arithmeticalprogression.

For purposes of illustration, some embodiments may be described in thecontext of an EWMA technique (which may employ a first-order infiniteimpulse response filter to apply weighting factors that may decreaseexponentially) and some specific values of parameters. However, othertechniques and or values may be obtained and/or used in accordance withthis disclosure.

Table 6 provides some example meanings of symbols used in Eq. 10 below.Although the embodiment of the workflow illustrated in Eq. 10 is notlimited to any particular implementation details, in some embodiments itmay be implemented, for example, by the optimal solution component 722illustrated in FIG. 7.

TABLE 6 Symbol Meaning t Epoch ID t (time sequence) |V|_(v, t) Workingvolume size of client v during epoch t. α The degree of weightingdecrease, which may be a constant smoothing factor between 0 and 1. Ahigher a may discount older observations faster. Some embodiments mayuse a value of α = 0.5. k number of epochs used for calculating theworking volume (For example, for k = 100, the most recent 100 epochs maybe used.)

In some embodiments, an EWMA technique may be used to calculate (e.g.,predict) the next epoch working volume for client v based on theprevious epoch working volume record for the client, as shown in Eq. 10.

|V| _(v,t+1)=α[|V| _(v,t)+(1−α)|V| _(v,t−1)+(1−α)² |V| _(v,t−2)+(1−α)³|V| _(v,t−3)+. . . ]  Eq. 10

Because Eq. 10 may be an infinite sum with decreasing terms, a workingvolume estimation technique in accordance with example embodiments ofthe disclosure may limit the number of terms used in Eq. 10 to reduceoverhead for computation and/or storage (e.g., storage used to recordI/O transaction history). For example, the number of recorded previousepochs may be limited to a value of “k”. That is, to approximate theprediction of working volume, terms after the k-th term may be omittedfrom Eq. 10. Thus, Eq. 10 may be simplified to Eq. 11.

$\begin{matrix}{{V}_{v,{t + 1}} = {\alpha\left\{ {\sum\limits_{k \in {\lbrack{0,k_{\max}}\rbrack}}\left\lbrack {\left( {1 - \alpha} \right)^{k}{V}_{v,{t - k}}} \right\rbrack} \right\}}} & {{Eq}.\mspace{11mu} 11}\end{matrix}$

In some embodiments, during the initialization phase, few data points ofworking volume size may be available. Thus, during the initializationphase, the working volume may be calculated, for example, from the firstfew observations and/or an average of 4-5 PMSW epochs.

6. Partition and Content Update

After the strategy selector subsystem 718 determines a partitioningstrategy for a storage tier (e.g., a top-tier which may operate as astorage cache), it may be transferred to the partition operatorsubsystem 724 for implementation. In some embodiments, implementing apartitioning strategy may involve eviction and/or fetching operations.

6.1 Partition and Content Update Workflow

FIG. 14 illustrates an example embodiment of a partition and contentupdate workflow in accordance with example embodiments of thedisclosure. Although the embodiment of the workflow illustrated in FIG.14 is not limited to any particular implementation details, in someembodiments it may be implemented, for example, by the partitionercomponent 726 illustrated in FIG. 7. In some embodiments, the terms“cache size”, “cache space”, “new partition”, and “quota” may be usedinterchangeably.

The workflow illustrated in FIG. 14 may begin at operation 1402 wherethe size of a client's new partition may be compared to the size of itscurrent partition. In some embodiments, the comparison may result in oneof three cases. (Case 1) If the client's new partition is smaller thanits previous size, the workflow may proceed to operation 1404 where theworkflow may evict one or more of the client's cached slots, then shrinkthe partition to the new size., (Case 2) If the client's new partitionis equal to its previous size, the workflow may proceed to operation1406 where it may leave the partition at its current size. (Case 3) Ifthe client's new partition is larger than its previous size, theworkflow may proceed to operation 1408 where the workflow may increasethe size of the partition. In Case 3, there may be two options for thenew space in the client's partition. (Option 1) The workflow may proceedto operation 1410 which may be described as a passive option. In thepassive option, the new space in the client's partition is initiallyleft blank. The new blank space may gradually fill as new I/O requestsmay progressively fill the blank space. (Option 2) The workflow mayproceed to operation 1412 which may be described as a proactive option.The workflow may proactively prefetch data from another far of storage(e.g., the second tier if the cache is the top-tier) and copying it tothe first tier to fill in the blank space. For example, in someembodiments, the workflow may copy warm data that may not be cached,but, based on I/O history, may be frequently used, to the blank space inthe client's new partition. In some embodiments, the workflow mayproceed to operation 1414, before filling in all of the new blank spacewhere a prefetch size may be adaptively adjusted as described below.

After the re-partition is completed, the client may continue using itsnew quota until the next re-partition operation occurs.

In some embodiments, the decision to use passive option (Option 1) orthe proactive option (Option 2) may involve one or more tradeoffs thatmay be weighed based on the system implementation details. For example,the passive option may be simpler to implement and/or may involve lessoverhead because no data may be moved until it becomes the subject of anI/O request. However, with the passive option, the hit ratio of theclient whose cache space is increased may be underutilized because thebanks may not he filled, for example, until a future I/O burst fills theblanks. Additionally, or alternatively, some of the blank space may beunderutilized, for example, if the prediction of the burst is notaccurate and/or if the workload of the client changes for the nextepoch.

With the proactive option, the hit ratio for the client may increasebecause more data may he available in the cache. Moreover, proactivelyfilling the blank space may result in better utilization of the cachespace. However, the proactive option may result in higher overhead, forexample, because the system may perform one or more operations to select(including any calculations behind the selection) and transfer warm datathat had not previously been cached in the first tier. Moreover, theremay be a risk that some or all of the prefetched data may not be useful(e.g., reaccessed) in the next epoch, thereby resulting in extraoverhead.

Algorithm 6 illustrates some example operations of an embodiment ofpartition and content update workflow in accordance with exampleembodiments of the disclosure. Algorithm 6 may be performed, forexample, by the partitioner component 726 illustrated in FIG. 7. In theembodiment illustrated in Algorithm 6, code to process Case 1 may belocated at lines 4-6, code to process Case 2 may be located at lines7-10, and code to process Case 3 (including Option 1 and Option 2) maybe located at lines 11-18.

Algorithm 6  1 Subsystem_4_Partition_Operator:  2 Component_7_Partitioner:  3   Function Partition( ):  4    # Case 1:Client's new partition is smaller than its previous     size, then PMDSneeds to evict some of its cached slots, and     then shrink the size ofits partition.  5    if CacheQuota[clientID, nextEpoch] <CacheQuota[clientID,     curEpoch]:  6     cache.evictLeastRecentUsedDataToSecondTier(clientID,      CacheQuota[clientID, curEpoch]-CacheQuota[clientID,      nextEpoch])  7    # Case 2: Client's new partition is equal to itsprevious size,       PMDS keeps the current partition size.  8    elseif CacheQuota[clientID, nextEpoch] < CacheQuota[clientID,      curEpoch]:  9      # keep the current quota plan 10      pass 11   # Case 3: Client's new partition is greater than its previous size,      PMDS needs to increase the size of it and then we have two      options. 12    else if CacheQuota[clientID, nextEpoch] >CacheQuota[clientID,       curEpoch]: 13      if OPTION_1: 14        #passive operation: leave new slots blank 15        pass 16      else ifOPTION_2: 17        # proactive operation: prefetch some warm data fromthe         second tier to fill the blank 18       prefetchWarmDataFromSecondTier(clientID,        calPrefetchGranularity[clientID],         CacheQuota[clientID,nextEpoch]-CacheQuota[clientID,         curEpoch])

6.2 Adaptive Prefetch Size Adjustment

During a re-partitioning operation, if a client's new partition islarger than its previous size, and a partition manager system decides toproactively fill the blank space in the new partition (e.g., Case 3,Option 2 as described above), some embodiments of a partition mangersystem in accordance with example embodiments of the disclosure mayprovide an adaptive prefetch size adjustment (APSA) feature.

In some embodiments, an APSA feature may adjust the prefetch data size,for example, based on the top I/O-size popularity of each client in therecent epoch. For example, an APSA feature may adaptively and/orautomatically change prefetch data size. A prefetch technique may boostexecution performance, for example, by fetching data from the slowersecond-tier storage to the faster first-tier (cache tier) storage beforeit is actually needed. In a proactive operation option, data may beprefetched to fill in blank space of a newly assigned partition beforethe client requests the data (e.g., by making an I/O request for a cachelocation that was previously blank).

In some embodiments, if the majority of the I/Os from a client in therecent epoch are in the top I/O size (range) (e.g., 16 KB), then it maybe possible or likely that the client will follow the same or similarpattern in the future. Thus, prefetching warm data from the second tierusing the granularity of the top I/O size may help bypass the lookupprocess (which may be time consuming) in the second tier again if thereis a partial cache hit in the first tier in the future. A partial cachehit may occur when only part of the requested I/O is found in the cache,so a second tier lookup may be performed to find the remaining part ofthe requested I/O.

Thus, by performing a prefetch with a granularity of the top I/O size, apartition manager system in accordance with example embodiments of thedisclosure may help upgrade a partial cache hit to a full cache hit(e.g., the full requested I/O may be cached in the first tier).

Eq. 12 illustrates an embodiment of an equation that may be used toimplement adaptive prefetch size adjustment in accordance with exampleembodiments of the disclosure. Eq. 12 may be implemented, for example,by the partitioner component 726 illustrated in FIG. 7. Table 7 providessome example meanings of symbols used in Eq. 12, and may further explainthe relationships between a cache miss, a partial cache hit, and a fullcache hit.

In some embodiments, CachedIOReq may be characterized as the found data(cached in the first tier) of a new I/O request, which may be calculatedas follows based on Eq. 12.

CachedIOReq={x|x∈IOReq,x∈CashedIO}  Eq. 12

Where IOReq may refer to a set of data in the new I/O request, andCachedIO may refer to all data currently in the cache tier. The union ofIOReq and CachedIO sets may be the found data of this I/O in the cache.

In some embodiments, a preset prefetching amplification factor AF may beused, for example, to increase the flexibility of an APSA feature. As anexample, the amplification factor may be in the range [−100%, 100%]. Insome embodiments, the prefetching granularity may be further adjusted,for example, by setting AF to 5 percent such that it may prefetch anextra 5 percent of data compared to the “top I/O size”. This may beuseful, for example, where a storage device block and page alignment maybe taken into consideration, For example, a cross-block boundary I/O maytrigger more data access than its I/O request size.

TABLE 7 Cache status Subcategory Equations Cache miss N/A |CachedIOReq|= 0 Cache hit Partial cache hit |IOReq| > |CachedIOReq| Cache hit Fullcache hit |IOReq| ≤ |CachedIOReq|

Algorithm 7 illustrates some example operations of an embodiment of anadaptive prefetch size adjustment feature in accordance with exampleembodiments of the disclosure. Algorithm 7 may be performed, forexample, by the partitioner component 726 illustrated in FIG. 7. In theembodiment illustrated in Algorithm 7, code to implement anamplification factor AF may be located at lines 6-7.

Algorithm 7 1 Subsystem_4_Partition_Operator: 2 Component_7_Partitioner: 3   Function calPrefetchGranularity( ): 4   preset prefetching amplification factor AF 5    result=list( ) 6   for each clientID: 7    result[clientID]=getTopRangeIOSize(clientID)*(1+AF) 8    returnresult

FIG. 15 illustrates an example embodiment of an adaptive prefetch sizeadjustment method in accordance with example embodiments of thedisclosure. Although the embodiment illustrated in FIG. 15 is notlimited to any particular implementation details, in some embodiments itmay be implemented, for example, by the partitioner component 726illustrated in FIG. 7.

The method illustrated in FIG. 15 may begin at operation 1502 where themethod may obtain the prefetch amplification factor AF. At operation1504, the method may create a results list that may be used to store theresults of the adaptive prefetch size adjustment method. At operation1506, the method may iterate through the clients to determine the topI/O data sizes for each client. The result list may be returned atoperation 1508.

6.3 Data Selection for Filling Blank Cache Space

During a re-partitioning operation, if a client's new partition islarger than its previous size, and a partition manager system decides toproactively fill the blank space in the new partition (e.g., Case 3,Option 2 as described above), some embodiments of a partition mangersystem in accordance with example embodiments of the disclosure mayselect warm data to fill the blank space. In some embodiments, warm datamay not be cached, but based on I/O history, may be frequently used.

Algorithm 8 illustrates some example operations of an embodiment of awarm data selection method in accordance with example embodiments of thedisclosure. Algorithm 8 may be performed, for example, by thepartitioner component 726 illustrated in FIG. 7.

Algorithm 8  1 Subsystem_4_Partition_Operator:  2 Component_7_Partitioner:  3   FunctionprefetchWarmDataFromSecondTier(clientID, granularity,     blankSize):  4   =list( )  5    candidates.add(descendingSort(getGlobalHistoryRecord(), freq))  6    candidates.remove(cachedIOList)  7    for each candidatechunk in candidates:  8     if size(dataToPrefetch)<blankSize:  9     dataToAdd=getChunkWithGranularity(chunk,granularity) 10     dataToAdd=trim(dataToAdd, blankSize-size(dataToPrefetch)) 11     dataToPrefetch.addData(dataToAdd) 12     else: 13      break 14   prefetch(dataToPrefetch, secondTier, firstTier 15    return

In the embodiment illustrated in Algorithm 8, the code at lines 4-6 maycreate a list of candidates to store all descendingly sorted globalhistorical records (GHRs) in the second tier, which may be sorted, forexample, by the access frequency of each data chunk. Any chunk size maybe used, for example, 10 MB. In some embodiments, one or more slidingwindow techniques (e.g., EWMA) may be applied to the global history torecord I/O popularity statistics for bins that have been accessed inrecent epochs. Depending on the implementation details, this may reflectthe warm data access behavior more accurately.

As shown at line 6, by ignoring already cached data (cachedIOList), themethod may further iterate each chunk from hottest to coldest, and mayadd data to the fill into the dataToPrefetch list (in some embodiments,with consideration of amplified granularity calculated in Algorithm 7)until the blank space has been filled. If any blank space still exists,and the iterated data chunk is larger than the blank, the data chunk maybe trimmed to fill the blank to prevent wasting any blank space.

As shown at line 14, once the blank space is filled, the dataToPrefetchmay be sent to the prefetch function to perform the actual contentupdate from the second tier to the top-tier (cache tier). After thecontent update is completed, the top-tier storage may run as a cacheusing any caching algorithm such as LRU, application-aware cachereplacement (ACR), dock with adaptive replacement (CAR), and/or thelike. In some embodiments, write through and/or write back policies maybe supported.

FIG. 16 illustrates an example embodiment of an adaptive prefetch sizeadjustment method in accordance with example embodiments of thedisclosure. Although the embodiment illustrated in FIG. 16 is notlimited to any particular implementation details, in some embodiments itmay be implemented, for example, by the partitioner component 726illustrated in FIG. 7.

The method illustrated in FIG. 16 may begin at operation 1602 where alist of candidates may be created. At operation 1604, the list ofcandidates may be sorted, for example, based on frequency of use. Atoperation 1606, data that is already cached may be removed from the listof candidates. At operation 1608, a loop may begin for each candidatechunk. As long as the size of data to prefetch is less than the blanksize, operations 1610, 1612, and 1614 may add data chunks based on aselected granularity level, trim data that may be larger than a blank,and add the results to a list of data to add, respectively. At operation1608, once the size of data to prefetch is greater than or equal to theblank size, the method may proceed to operation 1616 which may implementa break operation, then proceed to operation 1618 where the prefetchdata is actually written to the cache. The method may terminate atoperation 1620.

7. Zoning Based on Preknowledge

In some embodiments, during a deployment stage (which may also bereferred to as an early stage or initiate stage), a partition managersystem in accordance with example embodiments of the disclosure may nothave adequate information to allocate one or more tiers of storage(e.g., a top-tier that may operate as a storage cache) to clients, Inthese situations, the partition manager system may use preknowledge ofclients' I/O patterns, for example, from a client pattern library,vendor selection hardware and/or software, SLAB, QoS, and/or the like tocreate a partition plan.

For example, in a game streaming datacenter application, preknowledgemay exist of the characterization of one or more hosted games such asfirst-person shot games which may involve frequent writes of smallrandom data, or car racing games that may involve frequent largesequential read I/Os. As another example, in a general-purposedatacenter, preknowledge may exist of workloads such as developersworking on virtual machines which may be write-intensive, and 3D videoediting on virtual machines may be CPU intensive and may have read-writeI/O mixed with high working volume and working set sizes.

Preknowledge such as this may be used to implement one or more zoningtechniques to separate workloads by multiple factors (e.g., read ratio,working set size, and/or the like of each workload according topreknowledge). Zoning may be physical, virtual, or any combinationthereof. In some embodiments, granularity for physical zoning may begreater than or equal to the size of a storage device, for example,grouping multiple storage devices into one zone. In some embodiments,granularity for virtual zoning may be less than or equal to the size ofa storage device, for example, zoning inside a storage device.

FIG. 17 illustrates an example embodiment of a preknowledge-based zoningmethod in accordance with example embodiments of the disclosure.Although the embodiment illustrated in FIG. 17 is not limited to anyparticular implementation details, in some embodiments it may beimplemented, for example, by the partitioner component 726 illustratedin FIG. 7.

In the embodiment illustrated in FIG. 17, preknowledge of the first fourclients (Client 1, Client 2, Client 3, and Client 4) may include averageread ratio, average working set size, and average working volume size asshown in table 1702. In some embodiments, averages may be based on asimple average of history records. Alternatively, or additionally,factors other than those listed in FIG. 17 may be used in the deploymentzoning process.

In the embodiment illustrated in FIG. 17, a top tier of storage 1704 maybe implemented with SSDs, and a second tier of storage 1706 may beimplemented with HDDs, but any other number and/or configuration oftiers and/or storage devices may be used.

In this example, the top tier of storage 1704 may have three zones: aread intensive zone for clients having workloads with a read ratio inthe range [90%, 100%], a read-write-mixed zone for clients havingworkloads with a read ratio in the range [10%, 90%), and awrite-intensive zone for clients having workloads with a read ratio inthe range [0%, 10%). These examples are only for purposes ofillustration, and other numbers of zones, ranges of values, and/or thelike may be used to create zones.

In the embodiment illustrated in FIG. 17, the partition manager systemmay proportionally adjust the size of each zone based on, for example,(1) the working set size for the read intensive zone, and/or (2) theworking volume size for the read-write-mixed zone and/or thewrite-intensive zone. In some embodiments, a proportional zoneadjustment as illustrated in FIG. 17 may be applied repeatedly (e.g.,periodically) to update the zone sizes.

In some embodiments, after the deployment is completed, a partitionmanager system in accordance with example embodiments of the disclosuremay run separately in each zone using any of the techniques disclosedherein. For example, the entire loop illustrated in FIG. 7 may runinside each zone.

Algorithm 9 illustrates some example operations of an embodiment of apreknowledge-based zoning method in accordance with example embodimentsof the disclosure. Algorithm 9 may be performed, for example, by thepartitioner component 726 illustrated in FIG. 7.

Algorithm 9 1 Function ZoneDeployment(preknowledgeTable,topTierStorage): 2  preset zoneReadRatioThresholds 3 zoneMemberPlan=compareReadRatioAndPlaceInZone(preknowledgeTable,  zoneReadRatioThresholds) 4  for zone in zonePlan: 5   for member inzone: 6    zoneAmount[zone]+=selectWorkingSetOrWorkingVolume(member) 7 zoneSizePlan=adjustZoneSizeProportioannyBasedOn(zoneAmount) 8 assignClientsToZone(zoneMemberPlan, ZoneSizePlan)

In the embodiment illustrated in Algorithm 9, the functionZoneDeployment may take two inputs preknowledgeTable and toprierStorageand may use a preset value zoneReadRatioThresholds as shown at line 2,which may be any number of zones, At line 3, the function may create thezoneMemberPlan by comparing the read ratio of each client in the preknowledge Table with the thresholds. At lines 4-6, it may then iteratethe zoneMemberPlan and calculate each zone's demand amount based on themember client's working set size (for a read intensive zone) or workingvolume size (for other zones). At line 7, the function may then adjustthe zone size proportionally based on the demand amount of each zone. Atline 8, the function may assign clients to zones based on thezoneMemberPlan and ZoneSizePlan.

In some embodiments, and depending on the implementation details, apreknowledge-based zoning method in accordance with example embodimentsof the disclosure may: (1) reduce device-side write amplification; (2)reduce over-provisioning (which may be similar to early replacementbecause in both cases the host may consume more devices); (3) reducememory in storage devices (which may be relatively expensive); (4)improve latency, throughput, and/or predictability: and/or (5) enable asoftware eco-system because multiple stakeholders may benefit from oneor more improvements.

FIG. 18 illustrates an example embodiment of a preknowledge-based zoningworkflow in accordance with example embodiments of the disclosure.Although the embodiment illustrated in FIG. 18 is not limited to anyparticular implementation details, in some embodiments it may beimplemented, for example, by the partitioner component 726 illustratedin FIG. 7.

The embodiment illustrated in FIG. 18 may begin at operation 1802 wherea zone member plan may be created by comparing a read ratio of eachclient in a preknowledge table to zone read ratio thresholds. Atoperation 1804, the workflow may iterate the zone member plan andcalculate each zone's demand amount based on the member client's workingset size (for a read intensive zone) or working volume size (for otherzones). At operation 1806, the workflow may adjust the zone sizeproportionally based on the demand amount of each zone. At operation1808, the workflow may assign clients to zones based on the zone memberplan and the zone size plan.

FIG. 19 illustrates an embodiment of a method of operating a storagesystem in accordance with example embodiments of the disclosure. Themethod may begin at operation 1902. At operation 1904, the method mayallocate a first partition of a tier of storage resources to a firstclient, wherein the tier operates at least partially as a storage cache.At operation 1906, the method may allocate a second partition of thetier of the storage resources to a second client. At operation 1908, themethod may monitor a workload of the first client. At operation 1910,the method may monitor a workload of the second client. At operation1912, the method may reallocate the first partition of the tier of thestorage resources to the first client based on the monitored workload ofthe first client and the monitored workload of the second client. Themethod may end at operation 1914.

Embodiments disclosed above have been described in the context ofvarious implementation details, but the principles of this disclosureare not limited to these or any other specific details. For example,some functionality has been described as being implemented by certaincomponents, but in other embodiments, the functionality may bedistributed between different systems and components in differentlocations and having various user interfaces. Certain embodiments havebeen described as having specific processes, operations, etc., but theseterms also encompass embodiments in which a specific process, step, etc.may be implemented with multiple processes, operations, etc., or inwhich multiple processes, operations, etc. may be integrated into asingle process, step, etc. A reference to a component or element mayrefer to only a portion of the component or element. For example, areference to an integrated circuit may refer to all or only a portion ofthe integrated circuit, and a reference to a block may refer to theentire block or one or more subblocks. The use of terms such as “first”and “second” in this disclosure and the claims may only be for purposesof distinguishing the things they modify and may not indicate anyspatial or temporal order unless apparent otherwise from context. Insome embodiments, “based on” may refer to “based at least in part on.”In some embodiments, “allocate” may refer “allocate at least in part.” Areference to a first element may not imply the existence of a secondelement. Various organizational aids such as section headings and thelike may be provided as a convenience, but the subject matter arrangedaccording to these aids and the principles of this disclosure are notdefined or limited by these organizational aids.

The principles disclosed herein have independent utility and may beembodied individually, and not every embodiment may utilize everyprinciple. However, the principles may also be embodied in variouscombinations, some of which may amplify the benefits of the individualprinciples in a synergistic manner. Thus, the various details andembodiments described above may be combined to produce additionalembodiments according to the inventive principles of this patentdisclosure. Since the inventive principles of this patent disclosure maybe modified in arrangement and detail without departing from theinventive concepts, such changes and modifications are considered tofall within the scope of the following claims.

1. A method of operating a storage system, the method comprising:allocating a first partition of a tier of storage resources to a firstclient, wherein the tier operates at least partially as a storage cache;allocating a second partition of the tier of the storage resources to asecond client; monitoring a workload of the first client; monitoring aworkload of the second client; and reallocating the first partition ofthe tier of the storage resources to the first client based on theworkload of the first client and the workload of the second client. 2.The method of claim 1, wherein the first partition is reallocated basedon an input and/or output (I/O) demand of the workload of the firstclient.
 3. The method of claim 1, wherein the first partition isreallocated based on a performance change estimation of the workload ofthe first client.
 4. The method of claim 1, wherein the first partitionis reallocated based on a read-write ratio of the workload of the firstclient.
 5. The method of claim 1, wherein the first partition isreallocated based on a working set of the workload of the first client.6. The method of claim 1, wherein the first partition is reallocatedbased on a working volume of the workload of the first client.
 7. Themethod of claim 1, further comprising: determining a burst degree of theworkload of the first client and workload of the second client; anddetecting a burst of accesses of the tier of storage resources based onthe burst degree.
 8. The method of claim 1, further comprising:determining a first cache demand for the first client based on theworkload of the first client; and determining a second cache demand forthe second client based on the workload of the second client; whereinthe first partition is allocated to the first client based on the firstcache demand; and wherein the second partition is allocated to thesecond client based on the second cache demand.
 9. The method of claim1, further comprising: recording input and/or output (I/O) transactionsof the workload of the first client; determining a reuse distance basedon the recorded I/O transactions; and determining an expected cache hitratio based on the reuse distance.
 10. The method of claim 1, recordinginput and/or output (I/O) transactions of the workload of the firstclient; determining a weighted average of the recorded I/O transactions;and determining an expected working volume based on the weightedaverage.
 11. The method of claim 1, wherein reallocating the firstpartition comprises increasing the size of the first partition, themethod further comprising updating the first partition based on one ormore input and/or output (I/O) transactions of the workload of the firstclient.
 12. The method of claim 1, wherein reallocating the firstpartition comprises increasing the size of the first partition, themethod further comprising: determining a pattern of input and/or output(I/O) request sizes for the first client; and prefetching data for thefirst partition using a prefetch data size based on the pattern of I/Orequest sizes.
 13. The method of claim 1, wherein the first partition isallocated to the first client based on preknowledge of a characteristicof the first client.
 14. A method of partitioning a tier of storageresources, the method comprising: determining a read working volume anda write working volume of a first client of the tier and a second clientof tier; determining a workload type based on the read working volumeand the write working volume; and partitioning the tier of storageresources between the first client and the second client based on theworkload type.
 15. The method of claim 14, further comprising:determining a read ratio based on the read working volume and the writeworking volume; and determining the workload type based on the readratio.
 16. The method of claim 14, further comprising: determining aworking set size based on the workload type; and partitioning the tierof storage resources between the first client and the second clientbased on the working set size.
 17. The method of claim 14, furthercomprising: determining a working volume size based on the workloadtype; and partitioning the tier of storage resources between the firstclient and the second client based on the working volume size.
 18. Amethod of partitioning a tier of storage resources, the methodcomprising: determining a first partition plan for a first client and asecond client for the tier of storage resources; determining a firstexpected cache hit amount based on the first partition plan; determininga second partition plan for the first client and the second client forthe tier of storage resources; determining a second expected cache hitamount based on the second partition plan; and selecting one of thefirst partition plan or the second partition plan based on the firstexpected cache hit amount and the second expected cache hit amount. 19.The method of claim 18, further comprising: determining a first expectedhit ratio for the first client based on the first partition plan;determining a second expected hit ratio for the second client based onthe first partition plan; determining a first expected working volumefor the first client based on the first partition plan; and determininga second expected working volume for the second client based on thefirst partition plan.
 20. The method of claim 19, wherein determiningthe first expected cache hit amount comprises determining a weighted sumof the first expected hit ratio and the first expected working volumefor the first client and the second expected hit ratio and the secondexpected working volume for the second client.